Internet Explorer

Internet Explorer

Internet Explorer 10 in Windows 8
Original author(s)	Thomas Reardon
Developer(s)	Microsoft
Stable release	10.0.5 (May 14, 2013 (2013-05-14)) [±]
Preview release	N/A [±]
Development status	Active
Written in	C++
Operating system	Windows Mac OS (2.0-4.5) UNIX (4.0-5.01)
Included with	Windows 95 OSR 1 and later Windows NT 4 and later
Engine	Spyglass, Trident, Tasman
Available in	95 languages
Type	Web browser Feed reader
License	Proprietary software
Website	microsoft.com/ie
Standard(s)	HTML5, CSS3, RSS, Atom

Internet Explorer (formerly Microsoft Internet Explorer and Windows Internet Explorer, commonly abbreviated IE or MSIE) is a series of graphical web browsers developed by Microsoft and included as part of the Microsoft Windows line of operating systems, starting in 1995. It was first released as part of the add-on package Plus! for Windows 95 that year. Later versions were available as free downloads, or in service packs, and included in the OEM service releases of Windows 95 and later versions of Windows.

Internet Explorer is one of the most widely used web browsers, attaining a peak of about 95% usage share during 2002 and 2003. Its usage share has since declined with the launch of Safari (2003), Firefox (2004), and Google Chrome (2008), each of which now has significant market share. Estimates for Internet Explorer's overall market share range from 27.4% to 54.13%, as of October 2012 (browser market share is notoriously difficult to calculate). Microsoft spent over US$100 million per year on Internet Explorer in the late 1990s, with over 1000 people working on it by 1999.

Since its first release, Microsoft has added features and technologies such as basic table display (in version 1.5); XMLHttpRequest (in version 5), which aids creation of dynamic web pages; and Internationalized Domain Names (in version 7), which allow Web sites to have native-language addresses with non-Latin characters. The browser has also received scrutiny throughout its development for use of third-party technology (such as the source code of Spyglass Mosaic, used without royalty in early versions) and security and privacy vulnerabilities, and both the United States and the European Union have alleged that integration of Internet Explorer with Windows has been to the detriment of other browsers.

The latest stable release is Internet Explorer 10, with a new interface allowing for use as both a desktop application, and as a Windows 8 application.

Versions of Internet Explorer for other operating systems have also been produced, including an Xbox 360 version called Internet Explorer for Xbox and an embedded OEM version called Pocket Internet Explorer, later rebranded Internet Explorer Mobile, which is currently based on Internet Explorer 9 and made for Windows Phone, Windows CE, and previously, based on Internet Explorer 7 for Windows Mobile. It remains in development alongside the desktop versions. Internet Explorer for Mac and Internet Explorer for UNIX ( Solaris and HP-UX) have been discontinued.

History

The Internet Explorer project was started in the summer of 1994 by Thomas Reardon, using source code from Spyglass, Inc. Mosaic, an early commercial web browser with formal ties to the pioneering NCSA Mosaic browser. In late 1994, Microsoft licensed Spyglass Mosaic for a quarterly fee plus a percentage of Microsoft's non-Windows revenues for the software. Although bearing a name similar to NCSA Mosaic, Spyglass Mosaic had used the NCSA Mosaic source code sparingly. Microsoft was sued by Synet Inc. in 1996 over the trademark infringement.

Internet Explorer 1

The first version of Internet Explorer (later referred to as Internet Explorer 1) made its debut on 16 August 1995. It was a reworked version of Spyglass Mosaic, which Microsoft had licensed, like many other companies initiating browser development, from Spyglass Inc. It came with Microsoft Plus! for Windows 95 and the OEM release of Windows 95, and was installed as part of the Internet Jumpstart Kit in Plus!. The Internet Explorer team began with about six people in early development. Internet Explorer 1.5 was released several months later for Windows NT and added support for basic table rendering. By including it free of charge on their OS, they did not have to pay royalties to Spyglass Inc, resulting in a lawsuit and a multi-million USD settlement.

Internet Explorer 2

Internet Explorer 2 was released for Windows 95, Windows NT 3.5, and NT 4.0 on 22 November 1995 (following a 2.0 beta in October). It featured support for SSL, cookies, VRML, RSA, and Internet newsgroups. Version 2 was also the first release for Windows 3.1 and Macintosh System 7.0.1 (PPC or 68k), although the Mac version was not released until January 1996 for PPC, and April for 68k. Version 2.1 for the Mac came out in August 1996, although by this time, Windows was getting 3.0. Version 2 was included in Windows 95 OSR 1 and Microsoft's Internet Starter Kit for Windows 95 in early 1996. It launched with twelve languages, including English, but by April 1996, this expanded to 24, 20, and 9 for Win 95, Win 3.1, and Mac, respectively. The 2.0i version supported double-byte character-set.

Internet Explorer 3

Market share history snapshot for February 2005
IE4: 0.07%
IE5: 6.17%
IE6: 82.79%

Internet Explorer 3 was released on 13 August 1996 and went on to be much more popular than its predecessors. Internet Explorer 3 was the first major browser with CSS support, although this support was only partial. It also introduced support for ActiveX controls, Java applets, inline multimedia, and the PICS system for content metadata. Version 3 also came bundled with Internet Mail and News, NetMeeting, and an early version of the Windows Address Book, and was itself included with Windows 95 OSR 2. Version 3 proved to be the first more popular version of Internet Explorer, bringing with it increased scrutiny. In the months following its release, a number of security and privacy vulnerabilities were found by researchers and hackers. This version of Internet Explorer was the first to have the 'blue e' logo. The Internet Explorer team consisted of roughly 100 people during the development of three months. The first major IE security hole, the Princeton Word Macro Virus Loophole, was discovered on 22 August 1996 in IE3. Backwards compatibility was handled by allowing users who upgraded to IE3 to still use the last IE, because the installation converted the previous version to a separate directory.

Internet Explorer 4

Market share history snapshot for October 2008
IE4: 0.01%
IE5: 0.20%
IE6: 37.01%
IE7: 35.81%

Internet Explorer 4, released in September 1997, deepened the level of integration between the web browser and the underlying operating system. Installing version 4 on a Windows 95 or Windows NT 4 machine and choosing Windows Desktop Update would result in the traditional Windows Explorer being replaced by a version more akin to a web browser interface, as well as the Windows desktop itself being web-enabled via Active Desktop. The integration with Windows, however, was subject to numerous packaging criticisms (see United States v. Microsoft). This option was no longer available with the installers for later versions of Internet Explorer, but was not removed from the system if already installed. Internet Explorer 4 introduced support for Group Policy, allowing companies to configure and lock down many aspects of the browser's configuration as well as support for offline browsing. Internet Mail and News was replaced with Outlook Express, and Microsoft Chat and an improved NetMeeting were also included. This version was also included with Windows 98. New features that allowed users to save and retrieve posts in comment forms were added, but they are not used today. Internet Explorer 4.5 offered new features such as easier 128-bit encryption. It also offered a dramatic stability improvement over prior versions, particularly the 68k version, which was especially prone to freezing.

Internet Explorer 5

Internet Explorer 5, launched on 18 March 1999, and subsequently included with Windows 98 Second Edition and bundled with Office 2000, was another significant release that supported bi-directional text, ruby characters, XML, XSLT, and the ability to save web pages in MHTML format. IE5 was bundled with Outlook Express 5. Also, with the release of Internet Explorer 5.0, Microsoft released the first version of XMLHttpRequest, giving birth to Ajax (even though the term "Ajax" was not coined until years later). It was the last with a 16-bit version. Internet Explorer 5.01, a bug fix version included in Windows 2000, was released in December 1999. Internet Explorer 5.5 followed in July 2000, improving its print preview capabilities, CSS and HTML standards support, and developer APIs; this version was bundled with Windows Me. However, version 5 was the last version for Mac and UNIX. Version 5.5 was the last to have Compatibility Mode, which allowed Internet Explorer 4 to be run side by side with the 5.x. The IE team consisted of over 1,000 people by 1999, with funding on the order of US$100 million per year.

Internet Explorer 6

Internet Explorer 6 was released on 27 August 2001, a few months before Windows XP. This version included DHTML enhancements, content restricted inline frames, and partial support of CSS level 1, DOM level 1, and SMIL 2.0. The MSXML engine was also updated to version 3.0. Other new features included a new version of the Internet Explorer Administration Kit (IEAK), Media bar, Windows Messenger integration, fault collection, automatic image resizing, P3P, and a new look-and-feel that was in line with the Luna visual style of Windows XP, when used in Windows XP. Internet Explorer 6.0 SP1 offered several security enhancements and coincided with the Windows XP SP1 patch release. In 2002, the Gopher protocol was disabled, and support for it was dropped in Internet Explorer 7. Internet Explorer 6.0 SV1 came out on 6 August 2004 for Windows XP SP2 and offered various security enhancements and new colour buttons on the user interface. Internet Explorer 6 updated the original 'blue e' logo to a lighter blue and more 3D look. Microsoft now considers IE6 to be an obsolete product and recommends that users upgrade to Internet Explorer 8. Some corporate IT users have not upgraded despite this, in part because some still use Windows 2000, which will not run Internet Explorer 7 or above. Microsoft has launched a website, http://ie6countdown.com/, with the goal of getting Internet Explorer 6 usage to drop below 1 percent worldwide. Its usage is 6% globally as of October 2012, and depending to the country the usage differs heavily: while the usage in Norway is 0.1%, it is 21.3% in the People's Republic of China. On 3 January 2012, Microsoft announced that usage of IE6 in the United States had dropped below 1%.

Internet Explorer 7

Internet Explorer 7 was released on 18 October 2006. It includes bug fixes, enhancements to its support for web standards, tabbed browsing with tab preview and management, a multiple-engine search box, a web feeds reader, Internationalized Domain Name support (IDN), Extended Validation Certificate support, and an anti-phishing filter. With IE7, Internet Explorer has been decoupled from the Windows Shell—unlike previous versions, the Internet Explorer ActiveX control is not hosted in the Windows Explorer process, but rather runs in a separate Internet Explorer process. It is included with Windows Vista and Windows Server 2008, and is available for Windows XP Service Pack 2 and later, and Windows Server 2003 Service Pack 1 and later. The original release of Internet Explorer 7 required the computer to pass a Windows Genuine Advantage validation check prior to installing, but on October 5, 2007, Microsoft removed this requirement. As some statistics show, by mid-2008, Internet Explorer 7 market share exceeded that of Internet Explorer 6 in a number of regions.

Internet Explorer 8

Internet Explorer 8 was released on 19 March 2009. It had been in development since August 2007 at the latest. On 5 March 2008, the first public beta (Beta 1) was released to the general public. On 27 August 2008, the second public beta (Beta 2) was released. It is supported in Windows XP SP2 and SP3, Windows Server 2003 SP2, Windows Vista, Windows 7, and Windows Server 2008 on both 32-bit and 64-bit architectures. Internet Explorer 8 (IE8) RC1 was released on 26 January 2009. Internet Explorer 8 "Final" was released on March 19, 2009. Security, ease of use, and improvements in RSS, CSS, and Ajax support are Microsoft's priorities for IE8. It includes much stricter compliance with web standards, including a planned full Cascading Style Sheets 2.1 compliance for the release version. All of these changes allowed Internet Explorer 8 to pass the Acid2 test. However, to prevent compatibility issues, IE8 also includes the IE7 rendering behaviour. Sites that expect IE7 quirks can disable IE8's breaking changes by including a meta element in the HEAD section of the HTML document. IE8 also includes numerous improvements to JavaScript support as well as performance improvements, although it still does not pass the Acid3 test, with version 8.0 scoring 20/100. It includes support for accelerators, which allow supported web applications to be invoked without explicitly navigating to them; and WebSlices, which allows portions of a page to be subscribed to and monitored from a redesigned Favourites Bar. Other features include InPrivate privacy features and a SmartScreen phishing filter.

Internet Explorer 9

Internet Explorer 9 was released on 14 March 2011. Development for Internet Explorer 9 began shortly after the release of Internet Explorer 8. Microsoft first announced Internet Explorer 9 at PDC 2009, and spoke mainly about how it takes advantage of hardware acceleration in DirectX to improve the performance of web applications and quality of web typography. At MIX 10, Microsoft showed and publicly released the first Platform Preview for Internet Explorer 9, a frame for IE9's engine not containing any UI of the browser. Leading up to the release of the final browser, Microsoft released updated platform previews, each featuring improved JavaScript compiling (32-bit version), improved scores on the Acid3 test, as well as additional HTML5 standards support, approximately every 6 weeks. Ultimately, eight platform previews were released. The first public beta was released at a special event in San Francisco, which was themed around "the beauty of the web". The release candidate was released on February 10, 2011, and featured improved performance, refinements to the UI, and further standards support. The final version was released during the South by Southwest (SXSW) music and film festival in Austin, Texas, on 14 March 2011.

Internet Explorer 9 is only supported on Windows Vista SP2, Windows 7, and Windows Server 2008. It supports several CSS 3 properties (including border-radius, box-shadow, etc.), and embedded ICC v2 or v4 colour profiles support via Windows Colour System. The 32-bit version has faster JavaScript performance, this being due to a new JavaScript engine called "Chakra". It also features hardware accelerated graphics rendering using Direct2D, hardware-accelerated text rendering using DirectWrite, hardware-accelerated video rendering using Media Foundation, imaging support provided by Windows Imaging Component, and high fidelity printing powered by the XPS print pipeline. IE9 also supports the HTML5 video and audio tags and the Web Open Font Format. Internet Explorer 9 initially scored 95/100 on the Acid3 test, but has scored 100/100 since the test was updated in September 2011.

Internet Explorer was to be omitted from Windows 7 and Windows Server 2008 R2 in Europe, but Microsoft ultimately included it, with a browser option screen allowing users to select any of several web browsers (including Internet Explorer).

Internet Explorer is now available on Xbox 360 with Kinect support, as of October 2012.

Internet Explorer 10

Internet Explorer 10 became generally available on October 26, 2012 alongside Windows 8 and Windows Server 2012. It became available for Windows 7 on February 26, 2013. Microsoft announced Internet Explorer 10 in April 2011 at MIX 11 in Las Vegas, releasing the first Platform Preview at the same time. At the show, it was said that Internet Explorer 10 was about 3 weeks in development. This release further improves upon standards support, including CSS3 gradients. Internet Explorer 10 drops support for Windows Vista and will only run on Windows 7 and later. Internet Explorer 10 Release Preview was also released on the Windows 8 Release Preview platform.

Internet Explorer 11

A build of Internet Explorer 11 is featured in a build of Windows 8's "Blue" update which leaked in March 2013. The build includes an incomplete mechanism for syncing tabs, and now identifies as being "like Gecko" in its user agent. The latest build also include the Metro-style Developer Tools with additional features like testing for Mobile version of responsive designs. Also support for other modern features ( WebGL, SPDY, enhancements in JavaScript object model) was spotted.

Features

Internet Explorer has been designed to view a broad range of web pages and provide certain features within the operating system, including Microsoft Update. During the heyday of the browser wars, Internet Explorer superseded Netscape only when it caught up technologically to support the progressive features of the time.

Standards support

Internet Explorer, using the Trident layout engine:

• supports HTML 4.01, HTML 5, CSS Level 1, Level 2 and Level 3, XML 1.0, and DOM Level 1, with minor implementation gaps.
• fully supports XSLT 1.0 as well as an obsolete Microsoft dialect of XSLT often referred to as WD-xsl, which was loosely based on the December 1998 W3C Working Draft of XSL. Support for XSLT 2.0 lies in the future: semi-official Microsoft bloggers have indicated that development is underway, but no dates have been announced.
• Almost full conformance to CSS 2.1 has been added in the Internet Explorer 8 release. The trident rendering engine in Internet Explorer 9 in 2011 scores highest in the official W3C conformance test suite for CSS 2.1 of all major browsers.
• supports XHTML in Internet Explorer 9 ( Trident version 5.0). Prior versions can render XHTML documents authored with HTML compatibility principles and served with a text/html MIME-type.
• supports a subset of SVG in Internet Explorer 9 ( Trident version 5.0), excluding SMIL, SVG fonts and filters.

Internet Explorer uses DOCTYPE sniffing to choose between standards mode and a " quirks mode" in which it deliberately mimicks nonstandard behaviours of old versions of MSIE for HTML and CSS rendering on screen (Internet Explorer always uses standards mode for printing). It also provides its own dialect of ECMAScript called JScript.

Internet Explorer had been subjected to criticism by W3C over its limited support for SVG promoted by W3C.

Non-standard extensions

Internet Explorer has introduced an array of proprietary extensions to many of the standards, including HTML, CSS, and the DOM. This has resulted in a number of web pages that appear broken in standards-compliant web browsers and has introduced the need for a " quirks mode" to allow for rendering improper elements meant for Internet Explorer in these other browsers.

Internet Explorer has introduced a number of extensions to the DOM that have been adopted by other browsers. These include the innerHTML property, which provides access to the HTML string within an element ; the XMLHttpRequest object, which allows the sending of HTTP request and receiving of HTTP response, and is essential to the AJAX web programming technique ; and the designMode attribute of the contentDocument object, which enables rich text editing of HTML documents . Some of these functionalities were not possible until the introduction of the W3C DOM methods. Its Ruby character extension to HTML is also accepted as a module in W3C XHTML 1.1, though it is not found in all versions of W3C HTML.

Microsoft submitted several other features of IE for consideration by the W3C for standardization. These include the 'behaviour' CSS property, which connects the HTML elements with JScript behaviours (known as HTML Components, HTC); HTML+TIME profile, which adds timing and media synchronization support to HTML documents (similar to the W3C XHTML+SMIL), and the VML vector graphics file format. However, all were rejected, at least in their original forms; VML was subsequently combined with PGML (proposed by Adobe and Sun), resulting in the W3C-approved SVG format, currently one of the few vector image formats being used on the web, which IE did not support until version 9.

Other non-standard behaviours include: support for vertical text, but in a syntax different from W3C CSS3 candidate recommendation, support for a variety of image effects and page transitions, which are not found in W3C CSS, support for obfuscated script code, in particular JScript.Encode. Support for embedding EOT fonts in web pages.

Favicon

The favicon (short for "favorites icon") introduced by Internet Explorer is now also supported and extended in other browsers. It allows web pages to specify a 16-by-16 pixel image for use in bookmarks. In IE, support was, and still is, provided only for the native Windows ICO format; in other browsers it has now been extended to other types of images such as PNG and GIF.

Usability and accessibility

Internet Explorer makes use of the accessibility framework provided in Windows. Internet Explorer is also a user interface for FTP, with operations similar to that of Windows Explorer. Pop-up blocking and tabbed browsing were added respectively in Internet Explorer 6 and Internet Explorer 7. Tabbed browsing can also be added to older versions by installing MSN Search Toolbar or Yahoo Toolbar.

Cache

Internet Explorer caches visited content in the Temporary Internet Files folder to allow quicker access (or offline access) to previously visited pages. The content is indexed in a database file, known as Index.dat. Multiple Index.dat files exist which index different content—visited content, web feeds, visited URLs, cookies, etc.

Prior to IE7, clearing the cache used to clear the index but the files themselves were not reliably removed, posing a potential security and privacy risk. In IE7 and later, when the cache is cleared, the cache files are more reliably removed, and the index.dat file is overwritten with null bytes.

Caching has been improved in IE9.

Group Policy

Internet Explorer is fully configurable using Group Policy. Administrators of Windows Server domains (for domain-joined computers) or the local computer can apply and enforce a variety of settings on computers that affect the user interface (such as disabling menu items and individual configuration options), as well as underlying security features such as downloading of files, zone configuration, per-site settings, ActiveX control behaviour and others. Policy settings can be configured for each user and for each machine. Internet Explorer also supports Integrated Windows Authentication.

Architecture

Internet Explorer uses a componentized architecture built on the Component Object Model (COM) technology. It consists of several major components, each of which is contained in a separate Dynamic-link library (DLL) and exposes a set of COM programming interfaces hosted by the Internet Explorer main executable, iexplore.exe:

• WinInet.dll is the protocol handler for HTTP, HTTPS and FTP. It handles all network communication over these protocols.
• URLMon.dll is responsible for MIME-type handling and download of web content, and provides a thread-safe wrapper around WinInet.dll and other protocol implementations.
• MSHTML.dll houses the Trident rendering engine introduced in Internet Explorer 4, which is responsible for displaying the pages on-screen and handling the Document Object Model of the web pages. MSHTML.dll parses the HTML/CSS file and creates the internal DOM tree representation of it. It also exposes a set of APIs for runtime inspection and modification of the DOM tree. The DOM tree is further processed by a layout engine which then renders the internal representation on screen.
• IEFrame.dll contains the user interface and window of IE in Internet Explorer 7 and above.
• ShDocVw.dll provides the navigation, local caching and history functionalities for the browser.
• BrowseUI.dll is responsible for the browser user interface, including the browser chrome, which houses all the menus and toolbars.

Internet Explorer does not include any native scripting functionality. Rather, MSHTML.dll exposes an API that permit a programmer to develop a scripting environment to be plugged-in and to access the DOM tree. Internet Explorer 8 includes the bindings for the Active Scripting engine, which is a part of Microsoft Windows and allows any language implemented as an Active Scripting module to be used for client-side scripting. By default, only the JScript and VBScript modules are provided; third party implementations like ScreamingMonkey (for ECMAScript 4 support) can also be used. Microsoft also makes available the Microsoft Silverlight runtime that allows CLI languages, including DLR-based dynamic languages like IronPython and IronRuby, to be used for client-side scripting.

Internet Explorer 8 introduces some major architectural changes, called Loosely Coupled IE (LCIE). LCIE separates the main window process (frame process) from the processes hosting the different web applications in different tabs (tab processes). A frame process can create multiple tab processes, each of which can be of a different integrity level; each tab process can host multiple web sites. The processes use asynchronous Inter-Process Communication to synchronize themselves. Generally, there will be a single frame process for all web sites. In Windows Vista with Protected Mode turned on, however, opening privileged content (such as local HTML pages) will create a new tab process as it will not be constrained by Protected Mode.

Extensibility

Internet Explorer exposes a set of Component Object Model (COM) interfaces that allow other components to extend the functionality of the browser. Extensibility is divided into two types: Browser extensibility and Content extensibility. The browser extensibility interfaces can be used to plug in components to add context menu entries, toolbars, menu items or Browser Helper Objects (BHO). BHOs are used to extend the feature set of the browser, whereas the other extensibility options are used to expose the feature in the UI. Content extensibility interfaces are used by different content-type handlers to add support for non-native content formats. BHOs not only have unrestricted access to the Internet Explorer DOM and event model, they also can access the filesystem, registry and other OS components. Content extensibility can be either in terms of Active Documents (Doc Objects) (e.g., SVG or MathML) or ActiveX controls. ActiveX controls are used for content handlers that render content embedded within an HTML page (e.g., Adobe Flash or Microsoft Silverlight). Doc objects are used when the content type will not be embedded in HTML (e.g., Microsoft Word, PDF or XPS). In fact, the Trident rendering engine is itself exposed as a Doc object, so HTML in itself is treated as an Active Document.

Internet Explorer add-on components run with the same privileges as the browser itself, unlike client-side scripts that have a very limited set of privileges. Add-ons can be installed either locally, or directly by a web site. Since the add-ons have a more privileged access to the system, malicious add-ons can and have been used to compromise the security of the system. Internet Explorer 6 Service Pack 2 onwards provide various safeguards against this, including an Add-on Manager for controlling ActiveX controls and Browser Helper Objects and a "No Add-Ons" mode of operation as well as greater restrictions on sites installing add-ons.

Internet Explorer 9 introduced a new component — Add-on Performance Advisor. Add-on Performance Advisor shows a notification when one or more of installed add-ons exceed a pre-set performance threshold. The notification appears in the Notification Bar when the user launches the browser.

Internet Explorer itself can be hosted by other applications via a set of COM interfaces. This can be used to embed the browser functionality inside the application. Also, the hosting application can choose to host only the MSHTML.dll rendering engine, rather than the entire browser.

Security

Internet Explorer uses a zone-based security framework that groups sites based on certain conditions, including whether it is an Internet- or intranet-based site as well as a user-editable whitelist. Security restrictions are applied per zone; all the sites in a zone are subject to the restrictions.

Internet Explorer 6 SP2 onwards uses the Attachment Execution Service of Microsoft Windows to mark executable files downloaded from the Internet as being potentially unsafe. Accessing files marked as such will prompt the user to make an explicit trust decision to execute the file, as executables originating from the Internet can be potentially unsafe. This helps in preventing accidental installation of malware.

Internet Explorer 7 introduced the phishing filter, that restricts access to phishing sites unless the user overrides the decision. With version 8, it also blocks access to sites known to host malware. Downloads are also checked to see if they are known to be malware-infected.

In Windows Vista, Internet Explorer by default runs in what is called Protected Mode, where the privileges of the browser itself are severely restricted—it cannot make any system-wide changes. One can optionally turn this mode off but this is not recommended. This also effectively restricts the privileges of any add-ons. As a result, even if the browser or any add-on is compromised, the damage the security breach can cause is limited.

Patches and updates to the browser are released periodically and made available through the Windows Update service, as well as through Automatic Updates. Although security patches continue to be released for a range of platforms, most feature additions and security infrastructure improvements are only made available on operating systems which are in Microsoft's mainstream support phase.

On December 16, 2008, Trend Micro recommended users switch to rival browsers until an emergency IE patch was released to fix a potential security risk which "could allow outside users to take control of a person's computer and steal their passwords". Microsoft representatives countered this recommendation, claiming that "0.02% of internet sites" were affected by the flaw.

On December 17, 2008, a fix to the security problem above became available, with the release of the Security Update for Internet Explorer KB960714, which is available from Microsoft Windows Update's webpage. Microsoft has said that this update fixes the security risk found by Trend Micro the previous day.

In 2011, a report by Accuvant, funded by Google, rated the security (based on sandboxing) of Internet Explorer worse than Google Chrome but better than Mozilla Firefox.

Security vulnerabilities

Internet Explorer has been subjected to many security vulnerabilities and concerns: Much of the spyware, adware, and computer viruses across the Internet are made possible by exploitable bugs and flaws in the security architecture of Internet Explorer, sometimes requiring nothing more than viewing of a malicious web page in order to install themselves. This is known as a " drive-by install". There are also attempts to trick the user into installing malicious software by misrepresenting the software's true purpose in the description section of an ActiveX security alert.

A number of security flaws affecting IE originated not in the browser itself, but ActiveX-based add-ons used by it. Because the add-ons have the same privilege as IE, the flaws can be as critical as browser flaws. This has led to the ActiveX-based architecture being criticized for being fault-prone. By 2005, some experts maintained that the dangers of ActiveX have been overstated and there were safeguards in place. In 2006, new techniques using automated testing found more than a hundred vulnerabilities in standard Microsoft ActiveX components. Security features introduced in Internet Explorer 7 mitigated some of these vulnerabilities.

Internet Explorer in 2008 had a number of published security vulnerabilities. According to research done by security research firm Secunia, Microsoft did not respond as quickly as its competitors in fixing security holes and making patches available. The firm also reported 366 vulnerabilities in ActiveX controls, an increase from the prior year.

According to an October 2010 report in The Register, researcher Chris Evans had detected a known security vulnerability which, then dating back to 2008, had not been fixed for at least 600 days. Microsoft says that it had known about this vulnerability but it was of very low severity as the victim web site must be configured in a special way for this attack to be feasible at all.

In December 2010, researchers have been able to bypass the "Protected Mode" feature in Internet Explorer.

A security vulnerability exists in all versions of Internet Explorer higher than version 6, which allows the user's mouse cursor to be tracked by malicious display ads, even when Internet Explorer has been minimized. Microsoft has stated that it has no immediate plans to fix this vulnerability.

Vulnerability exploited in attacks on U.S. firms

In an advisory on January 14, 2010, Microsoft said that attackers targeting Google and other U.S. companies used software that exploits a security hole, which had already been patched, in Internet Explorer. The vulnerability affected Internet Explorer 6, IE7, and IE8 on Windows 7, Vista, Windows XP, Server 2003, and Server 2008 R2, as well as IE 6 Service Pack 1 on Windows 2000 Service Pack 4.

The German government warned users against using Internet Explorer and recommended switching to an alternative web browser, due to the major security hole described above that was exploited in Internet Explorer. The Australian and French Government issued a similar warning a few days later. The first browser they recommended was Mozilla Firefox, followed by Google Chrome.

Market adoption and usage share

The adoption rate of Internet Explorer seems to be closely related to that of Microsoft Windows, as it is the default web browser that comes with Windows. Since the integration of Internet Explorer 2.0 with Windows 95 OSR 1 in 1996, and especially after version 4.0's release, the adoption was greatly accelerated: from below 20% in 1996 to about 40% in 1998 and over 80% in 2000.

A CNN article noted at the release of Internet Explorer 4: "Microsoft's Internet Explorer has made inroads and various estimates put its share of the browser market 30 to 35 percent from about 10 percent a year ago." By 2002, Internet Explorer had almost completely superseded its main rival Netscape and dominated the market with up to 95 percent market share. After having fought and won the browser wars of the late 1990s, Internet Explorer gained almost total dominance of the browser market. Having attained a peak of about 95% during 2002 and 2003, its market share has since declined at a slow but steady pace. Usage is higher in Asia and lower in Europe.

Firefox 1.0 had surpassed Internet Explorer 5 in early 2005 with Firefox 1.0 at roughly 8 percent market share. An article notes at the release of Internet Explorer 7 in October 2006 that "IE6 had the lion's share of the browser market with 77.22%. Internet Explorer 7 had climbed to 3.18%, while Firefox 2.0 was at 0.69%."

Internet Explorer 7 was released at the same time as Firefox 2.0, and overtook Firefox 1.x by November 2006, at roughly 9% market share. Firefox 2.0 had overtaken 1.x by January 2007, but IE7 did not surpass IE6 until December 2007. By January 2008, their respective version market share stood at 43% IE7, 32% IE6, 16% FF2, 4% Safari 3 and both FF1.x and IE5 versions at less than half a percent.

Approximate usage over time based on various usage share counters averaged for the year overall, or for the fourth quarter, or for the last month in the year depending on availability of reference.

According to StatCounter Internet Explorer's marketshare fell below 50% in September 2010. In May 2012 it was announced that Google Chrome overtook Internet Explorer as the most used browser worldwide.

Desktop Market share by year and version

Approximate usage over time based on various usage share counters averaged for the year overall, or for the fourth quarter, or for the last month in the year depending on availability of reference.

	Total	IE10	IE9	IE8	IE7	IE6	IE5	IE4	IE3	IE2	IE1
2012	53.77%	0.14%	16.77%	25.87%	3.49%	6.81%	0%	0.01%	0%	0%	0%
2011	56.24%	-	5.30%	32.36%	7.00%	10.19%	0.01%	0%	0%	0%	0%
2010	60.04%	-	-	29.43%	11.61%	16.79%	0.02%	0%	0%	0%	0%
2009	66.92%	-	-	10.40%	26.10%	27.40%	0.08%	0%	0%	0%	0%
2008	72.65%	-	-	0.34%	46.06%	26.20%	0.15%	0.01%	0%	0%	0%
2007	78.60%	-	-	-	45.50%	32.64%	0.45%	0.01%	0%	0%	0%
2006	83.30%	-	-	-	3.49%	78.08%	1.42%	0.02%	0%	0%	0%
2005	87.12 %	-	-	-	-	82.71%	4.35%	0.06%	0%	0%	0%
2004	91.27 %	-	-	-	-	83.39%	7.77%	0.10%	0%	0%	0%
2003	94.43%	-	-	-	-	59.00%	34.00%	1.00%	0%	0%	0%
2002	93.94%	-	-	-	-	50.00%	41.00%	1.00%	0%	0%	0%
2001	90.83%	-	-	-	-	19.00%	68.00%	5.00%	0%	0%	0%
2000	83.95%	-	-	-	-	-	71.00%	13.00%	0%	0%	0%
1999	75.31%	-	-	-	-	-	41.00%	36.00%	1.00%	0%	0%
1998	45.00%	-	-	-	-	-	-	?	?	?	?
1997	39.40%	-	-	-	-	-	-	?	?	?	?
1996	20.00%	-	-	-	-	-	-	-	?	?	?
1995	2.90%	-	-	-	-	-	-	-	-	?	?

Industry adoption

Browser Helper Objects are also used by many search engine companies and third parties for creating add-ons that access their services, such as search engine toolbars. Because of the use of COM, it is possible to embed web-browsing functionality in third-party applications. Hence, there are a number of Internet Explorer shells, and a number of content-centric applications like RealPlayer also use Internet Explorer's web browsing module for viewing web pages within the applications.

OS compatibility

IE versions, over time, have had widely varying OS compatibility, ranging from being available for many platforms and several versions of Windows to only a few versions of Windows. Many versions of IE had some support for an older OS but stopped getting updates. The increased growth of the Internet in the 1990s and 2000s (decade) means that current browsers with small market shares have more total users than the entire market early on. For example, 90% market share in 1997 would be roughly 60 million users, but by the start of 2007 90% market share would equate to over 900 million users. The result is that later versions of IE6 had many more users in total than all the early versions put together.

The release of IE7 at the end of 2006 resulted in a collapse of IE6 market share; by February 2007, market version share statistics showed IE6 at about 50% and IE7 at 29%. Regardless of the actual market share, the most compatible version (across operating systems) of IE was 5.x, which had Mac OS 9 and Mac OS X, Unix, and most Windows versions available and supported for a short period in the late 1990s (although 4.x had a more unified codebase across versions). By 2007, IE had much narrower OS support, with the latest versions supporting only Windows XP Service Pack 2 and above. Internet Explorer 5.0, 5.5, 6.0, and 7.0 (Experimental) have also been unofficially ported to the Linux operating system from the project IEs4Linux.

	Years	Layout engine	Microsoft Windows														IBM OS/2 from 2.1	Apple Mac OS					Unix HP-UX Solaris
			8, WS 12	7, WS 08 R2	Vista, WS 08	WS 03	XP	Me	2000	98	NT 4.0	95	NT 3.51	NT 3.5	NT 3.1	3.1x		X PPC	7.6 to 9.2.2 PPC	7.5.x PPC	7.1 to 8.1 68K 7.1.2 PPC	7.0.1 68K
Years available	-	-	2012–present	2009–present	2006-2011	2003-2009	2001-2009 (SP 2/3)	2000-2001	2000-2001	1998-2001	1996-2001	1995-2000	1995-1999	1994-1996	1993-1995	1992-1999	1993-1996	2001 (PPC Systems only)	1997-1999	1994-1999	1992-1997	1991-1995	1996-1999
IE 10	2012	Trident 6.0	Included	Yes	No	No	No	No	No	No	No	No	No	No	No	No	No	No	No	No	No	No	No
IE 9	2011	Trident 5.0	No	Yes	Yes with Update	No	No	No	No	No	No	No	No	No	No	No	No	No	No	No	No	No	No
IE 8	2009	Trident 4.0	No	Included	Yes	Yes with SP2	Yes with SP2/3	No	No	No	No	No	No	No	No	No	No	No	No	No	No	No	No
IE 7	2006	Trident	No	No	Included	Yes with SP1/ 2	Yes with SP2/3&	No	No	No	No	No	No	No	No	No	No	No	No	No	No	No	No
IE 6	2001	Trident	No	No	No$	Included	Included	Yes 6.0 SP1	Yes 6.0 SP1	Yes 6.0 SP1	Yes 6.0 SP1	No	No	No	No	No	No	No	No	No	No	No	No
IE 5.5	2000	Trident	No	No	No	No	No***	Included	Yes	Yes	Yes	Yes 5.5 SP2	No	No	No	No	No	No	No	No	No	No	No
IE 5.0	1999	Trident Win Tasman Mac	No	No	No	No	No***	No	Included 5.01 SP4	Included with 98SE	Yes	Yes	Yes 16-bit	No	No	Yes 16-bit	No	Included 5.2.3 €	Included¥ 5.1.7 €	No	No	No	Yes 5.01 SP1
IE 4.5	1999	-	No	No	No	No	No	No	No	No	No	No	No	No	No	No	No	No	Included€	Yes	No	No	No
IE 4.0	1997	Trident	No	No	No	No	No***	No	No	Included	Yes	Included OSR2.5	Yes 16-bit	No	No	Yes 16-bit	No	No	Included€	Yes	Yes 4.01	No	Yes
IE 3.0	1996	-	No	No	No***	No	No***	No	No***	No	Yes	Included OSR2	Yes 16-bit	Yes 16-bit	No	Yes 16-bit	Win. 16-bit	No	Included€	Yes	Included€	No	Beta
IE 2.0	1995	-	No	No	No	No	No	No	No	No	Included	Included OSR1	Yes 16-bit	Yes 16-bit	Yes 16-bit	Yes 16-bit	Win. 16-bit	No	Yes	Yes	Yes£	Yes£ 2.0.1	No
IE 1.5	1996	Spyglass	No	No	No	No	No	No	No	No	Yes	Yes	Yes	Yes	No	No	No	No	No	No	No	No	No
IE 1.0	1995	Spyglass	No	No	No	No	No	No	No	No	No	Non-free Plus!	No	No	No	No	No	No	No	No	No	No	No

^* Internet Explorer 6 SP2 is only available as part of Windows XP SP2 or Windows Server 2003 SP1 or SP2.
^** The version of Internet Explorer included with Windows 95 varied by OSR release; 2.0 was included with OSR1, 3.0 was included with OSR2, and 4.0 was included with OSR2.5.
^*** No native support, but possible with third-party "Standalone" installer.
^& Final version of Windows XP Service Pack 3 does not include IE7.
^$ No native support, but possible with third party Standalone installer of IE6 Alpha. See also Internet Explorer Mobile. Non-desktop versions of IE have supported Windows CE also.
^£ Internet Explorer 2.0 and 2.0.1 requires System 7.0.1 or higher. Internet Explorer 2.1 requires System 7.1 or higher.
^€ Included Internet Explorer 3.01 in Mac OS 8.0 and Mac OS 8.1; Internet Explorer 4.01 in Mac OS 8.5 and 8.5.1; Internet Explorer 4.5 from Mac OS 8.6 to 9.0.4; Internet Explorer 5 from Mac OS 9.1 to 9.2.2 and Mac OS X v10.0; Internet Explorer 5.1 in Mac OS X v10.1; Internet Explorer 5.2 in Mac OS X v10.2.
^¥ Internet Explorer 5 Macintosh Edition requires Mac OS 7.6 or higher. Internet Explorer version 5.1; 5.1.4; 5.1.5; 5.1.6 and 5.1.7 requires Mac OS 8.0 or higher or Mac OS 7.6.1 with Appearance Manager.
¹⁶ 16-bit version

"Standalone" Internet Explorer

While Microsoft claims it is impossible to keep multiple versions of Internet Explorer on the same machine, some hackers have successfully separated several versions of Internet Explorer, making them standalone applications. A web developer, Joe Maddalone, is credited with finding a solution ( Multiple IEs in Windows Web Design). These are referred to as "standalone" IEs and go as far back as Internet Explorer version 3.

Standalone installers

Microsoft has discontinued standalone installers for Internet Explorer to the general public. However, there are unofficial procedures for downloading the complete install package. Internet Explorer standalone uses a feature introduced in Windows 2000 called DLL redirection to force it to load older DLLs than the ones installed on the system.

• IE Collection. An installer for the standalone versions of IE8.0, IE7.0, IE6.0, IE5.51, IE5.01, IE4.01, IE3.0, IE2.01, IE1.5, and IE1.0.
• Microsoft Support document, with instructions for downloading the entire set of installation files.

Alternative environments

It is also possible to install Internet Explorer in Wine (a compatibility layer):

• IEs4Linux automatically sets up Internet Explorer 5.0, 5.5, and 6.0 in Wine. Support for Internet Explorer 7 development was started August 2007, and stalled with the last package being available in 2008. That package used an IE7 rendering engine with the IE6 user interface. There was a blog post on January 5, 2011 announcing that the developers are working to support IE9 and will soon release a new version after almost 3 years of inactivity.
• IETester is a side-by-side compatibility checker for different versions of Internet Explorer. As of 2011, it is available from DebugBar as an alpha release. Its highest tester rating from the WineHQ profile has been Bronze.

As an alternative to using IE standalone, Microsoft now makes available Windows Virtual PC images containing copies of Microsoft Windows with IE installed:

• Windows XP SP3 with IE6 (with installers for IE7 and IE8)
• Windows Vista SP2 with IE7 (with installers for IE8 and IE9)
• Windows 7 SP1 with IE8 (with install files for IE9)
• Windows 7 IE9 + Tools Image

According to Microsoft's site, the images were last released on 16 August 2011 and expired on 17 November 2011.

Microsoft recommends this approach for web developers seeking to test their pages in the different versions of IE as the standalone versions are unsupported and may not work the same way as a properly installed copy of IE.

Versioning

Despite the official stance that only one version of Internet Explorer can be installed on the same machine, there are notable exceptions.

Early versions of Internet Explorer such as 5 had a compatibility mode to run Internet Explorer 4, though this feature was dropped (also, Internet Explorer for Mac users could still use 4.5 after installing IE 5). Internet Explorer 8 brought back the concept of a compatibility mode, but users cannot actually run the earlier versions of Internet Explorer.

Removal

While a major upgrade of Internet Explorer can be uninstalled in a traditional way if the user has saved the original application files for installation, the matter of uninstalling the version of the browser that has shipped with an operating system remains a controversial one.

The idea of removing a stock install of Internet Explorer from a Windows system was proposed during the United States v. Microsoft case. One of Microsoft's arguments during the trial was that removing Internet Explorer from Windows may result in system instability.

Removing Internet Explorer does have a number of consequences. Applications that depend on libraries installed by IE will fail to function correctly. The Windows help and support system will also not function due to the heavy reliance on HTML help files and components of IE. In versions of Windows before Vista, it is also not possible to run Microsoft's Windows Update or Microsoft Update with any other browser due to the service's implementation of an ActiveX control, which no other browser supports. In Windows Vista, Windows Update is implemented as a Control Panel applet.

With Windows 7, Microsoft added the ability to safely remove Internet Explorer 8 from Windows. Doing so removes the browser's executable file, unregisters its HTTP shell protocol handlers, and removes the icons from the user interface. However, it does leave behind DLLs and other files, in order to allow programs that use Trident to render pages to continue functioning correctly.