Internet Explorer (IE); formerly known as Microsoft Internet Explorer and Windows Internet Explorer, was a series of graphical web browsers made by Microsoft. It was part of the Microsoft Windows operating system, starting in 1995. It was first released as part of the add-on package Microsoft Plus! for Windows 95, that year. Later versions were free downloads, or in service packs, and included in releases of Windows 95 and later versions of Windows.

IE has been the most popular web browser since 1999, with up to 95% usage share during 2002/2003 with IE5 and IE6. Since its peak of popularity, its usage share has decreased to 55% due to rival web browsers, and is slowly trending downward. Microsoft spent over $100 million per year on IE[5] in the late 1990s, with over 1000 people working on it by 1999.[6]

The latest release is Internet Explorer 11. Internet Explorer was originally planned to be removed from Windows 7 and Windows Server 2008 R2 in Europe, but Microsoft later dropped the plans, and instead included a browser ballot screen with the products, allowing users to select a different web browser if they wish.[7][8][9][10]

Versions of Internet Explorer for other operating systems have also been produced, including an embedded OEM version called Internet Explorer for Windows CE (IE CE), available for WinCE based platforms and currently based on IE6; Internet Explorer for Pocket PC, later rebranded Internet Explorer Mobile, which is made for Windows Mobile and Windows CE and remains in development alongside the more advanced desktop versions; and the discontinued Internet Explorer for Mac and Internet Explorer for UNIX (Solaris and HP-UX).

The latest version of Windows, Windows 10, comes with a new web browser called Microsoft Edge. Internet Explorer 11 is still included, but is meant to be used for sites that do not work properly with the new rendering engine in Microsoft Edge.

The Internet Explorer project was started in the summer of 1994 by Thomas Reardon,[11] 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.[12] Although bearing a name similar to NCSA Mosaic, the Spyglass Mosaic had used the NCSA Mosaic source code sparingly.[13]

Internet Explorer 1 made its debut on August 16, 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. It was installed as part of the Internet Jumpstart Kit in Plus!.[14] The Internet Explorer team began with about six people in early development.[15][16] Internet Explorer 1.5 was released several months later for Windows NT and added support for basic table rendering. However, by including it for free on their OS, they did not have to pay royalties to Spyglass Inc., which resulted in a lawsuit and a multi-million USD settlement.

Internet Explorer 2 was released for Windows 95, Windows NT 3.5, and NT 4.0 on August 24, 1996 (following a 2.0 beta in November 1995). 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.[17] 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.[18] It launched with twelve languages including English but this expanded to 24, 20, and 9 for Win 95, Win 3.1, and Mac respectively by April 1996.[19] The 2.0i version supported double-byte character-set.[19]

Internet Explorer 3 was released on August 13, 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, which brought 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.[21] The Internet Explorer team consisted of roughly 100 people during the development of three months.[5] The first major IE security hole, the Princeton Word Macro Virus Loophole, was discovered on August 22, 1996 in IE3.[22] 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.[23]

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 also 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.[24] Internet Mail and News was replaced with Outlook Express, and Microsoft Chat and an improved NetMeeting were also included. This version also was included with Windows 98. New features were added that allow you to save and retrieve posts in comment forms which are still not being 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.[25][26][27]

Internet Explorer 5 was launched on March 18, 1999, later included with Windows 98 Second Edition and came with Office 2000. The creation of Internet Explorer 5 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, was released in December 1999. Windows 2000 includes this version. 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[29] to be run side by side with the 5.x.[21][30] The IE team consisted of over 1,000 people by 1999, with funding on the order of 100 million USD per year.[5][6]

Internet Explorer 6 was released on August 27, 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.[32] 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.[33] Internet Explorer 6.0 SV1[34] came out August 6, 2004 for Windows XP SP2 and offered various security enhancements and new color buttons on the user interface. IE6 updated the original 'blue e' logo to a lighter blue and more 3D look.[21] Microsoft now considers IE6 to be an obsolete product and recommends that users upgrade to IE8. Many corporate IT users have not upgraded despite this.[35]

Internet Explorer 7 was released on October 18, 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 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.[36]

Internet Explorer 8 was released on March 19, 2009. It had been in development since August 2007 at the latest.[37] On March 5, 2008, the first public beta (Beta 1) was released to the general public.[38] On August 27, 2008, the second public beta (Beta 2) was released.[39] 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 as well as 64-bit architectures.[40] Internet Explorer 8 (IE8) RC1 was released on January 26, 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.[41][42] It includes much stricter compliance with web standards, including a planned full Cascading Style Sheets 2.1 compliance for the release version.[43] All these changes allow Internet Explorer 8 to pass the Acid2 test.[44] However, to prevent compatibility issues, IE8 also includes the IE7 rendering behavior. 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,[43] although it still does not pass the Acid3 test, with version 8.0 scoring 20/100.[45] It includes support for Accelerators - which allow supported web applications to be invoked without explicitly navigating to them - and WebSlices - which allows portions of page to be subscribed to and monitored from a redesigned Favorites Bar.[43] Other features include InPrivate privacy features and SmartScreen phishing filter.[46]

Internet Explorer 9 was released on March 14, 2011.[47] It will have complete or nearly complete support for all CSS 3 selectors, border-radius CSS 3 property, faster JavaScript, embedded ICC v2 or v4 color profiles, and hardware accelerated rendering using Direct2D and DirectWrite. Microsoft has confirmed that Web Open Font Format (WOFF) will also be supported.[48] WOFF is "a strong favorite" for standardization by the Web Fonts Working Group of W3C.[49]
IE9 is supposed to fix many issues with Internet Explorer, including support of the CSS3 standard border-radius property, which means that people using IE9 will be able to see rounded corners, the same way people using Firefox can.[50]

Microsoft has continued to downplay the importance of passing the Acid3 test,[51]
but speculation that IE9 would support the SVG W3C recommendation was ignited when Microsoft announced they had joined the SVG Working Group.[52]
At MIX 10, the first IE9 Platform Preview was released, which featured support for CSS3 and SVG, a new JScript engine called Chakra, and a score of 55/100 on the Acid3 test, up from 20/100 for IE8. On May 5, 2010, the second IE9 Platform Preview was released, which featured a score of 68/100 on the Acid3 test and faster performance on the WebKit SunSpider JavaScript benchmark than the first IE9 Platform Preview. On June 23, 2010, the third IE9 Platform Preview was released, which scores 83/100 on the Acid3 test and introduced support for <audio>, <video>, and <canvas> elements and WOFF. On August 4, 2010, the fourth IE9 Platform Preview was released, which features a score of 95/100 on the Acid3 test and a faster JScript engine than the third IE9 Platform Preview. The final build of IE9 is expected to be released in 2011. Support for the HTML5 video and audio tags was also promised.[53][54]
Some industry experts predict that Microsoft will release IE9 as a major out-of-band version that is not tied to any particular version of Windows.[55]
According to the Internet Explorer 9 Test Drive page, "Internet Explorer 9 Test Drive". microsoft.com. the system requirements for IE9 are Windows Vista SP2 (with Platform Upgrade and IE8) or Windows 7.[56]
On August 12, 2010, Microsoft announced that the IE9 Public Beta would launch on September 15, 2010 at a special event in San Francisco linked to the idea of 'beauty of the web.'[57] It was also confirmed that the browser would only function with Windows Vista and Windows 7.[58] On September 15, 2010, Microsoft launched the IE9 Public Beta.[59]

Internet Explorer 10 does not work with Windows Vista, but only for Windows 7 and a future release of the Windows operating system.[60]

Internet Explorer 10 was released together with Windows 8 in 2012. Users of Windows 7 can download this version from February 2013.

Internet Explorer 11 was released in October 2013. It is the final Internet Explorer.[61]

Internet Explorer has been designed to view a broad range of web pages and to 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.[62]

Internet Explorer, using the Trident layout engine:

Internet Explorer uses DOCTYPE sniffing to choose between standards mode and a "quirks mode" in which it deliberately mimicks nonstandard behaviors 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 has been subjected to criticism by W3C over its limited support for SVG promoted by W3C.[65]

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 JScript which have been adopted by other browsers. These include the innerHTML property, which returns the HTML string within an element; the XMLHttpRequest object, which allows the sending of HTTP request and receiving of HTTP response; 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 'behavior' CSS property, which connects the HTML elements with JScript behaviors (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, however, 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, and which IE is now virtually unique in not supporting.[66]

Other non-standard behaviors include: support for vertical text, but in a syntax different from W3C CSS3 candidate recommendation; Support for a variety of image effects[67] and page transitions, which are not found in W3C CSS; Support for obfuscated script code, in particular JScript.Encode().[68] Support for embedding EOT fonts in web pages.[69]

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.

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.

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.[70]

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.

Internet Explorer is fully configurable using Group Policy. Administrators of Windows Server domains can apply and enforce a variety of settings 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 behavior and others. Policy settings can be configured for each user and for each machine. Internet Explorer also supports Integrated Windows Authentication.

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:[71]

[72]

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.[73]

Internet Explorer exposes a set of Component Object Model (COM) interfaces that allow other components to extend the functionality of the browser.[71] 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.[71] 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.[71] 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.[71]

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 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.[71]

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.[74][75]

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.[76] In 2006, new techniques using automated testing found more than a hundred vulnerabilities in standard Microsoft ActiveX components.[77] Security features introduced in then recently released 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.[78] The firm also reported 366 vulnerabilities in ActiveX controls, an increase from the prior year.

According to the latest information, Secunia reports that IE6 has 24 known unpatched vulnerabilities, IE7 has 11, and IE8 has 4. The most severe unpatched Secunia advisories affecting Microsoft Internet Explorer 6.x, 7.x, and 8.x with all vendor patches applied, are all rated Extremely critical. The oldest known unpatched vulnerabilities for IE6, IE7, and IE8 date from November 7, 2003, June 6, 2006, and February 26, 2007 respectively.

According to the latest information, security research firm SecurityFocus reports that IE6 has 396 known unpatched vulnerabilities, IE7 has 22, and IE8 has 25. The oldest known unpatched vulnerabilities for IE6, IE7, and IE8 date from November 20, 2000, May 17, 2007, and April 11, 2009 respectively.

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.[79]

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.[80] The Australian and French Government issued a similar warning a few days later.[81][82] The first browser they recommended was Mozilla Firefox, followed by Google Chrome.[83][84]

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."[85] 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. This is mainly due to the adoption of Mozilla Firefox, which statistics indicate is currently the most significant competition. Nevertheless, Internet Explorer remains the dominant web browser, with a global usage share of around 60% (though measurements vary). 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.[86]
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%."[87]

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.[88] Firefox 2.0 had overtaken 1.x by January 2007,[89] but IE7 did not surpass IE6 until December 2007.[90] 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.[91]

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.[92][93][94][95][96][97]

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.[93][94][95][96][97][98][99] IE was at its peak in 2003 with 94% of the worldwide internet browsers, but started falling in 2004 and since has hit a 2000s decade low in 2011 with only 49.7% of worldwide internet users.

The ActiveX extension mechanism is used by many public websites and web applications, including eBay.[source?] Similarly, 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.

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 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[100] users, but by the start of 2007 90% market share would equate to over 900 million users.[100] 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%.[101] 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.

[104][105]

* 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.

Ł 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 8.1; 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.

¥ 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.

16 16-bit version

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). 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. These are referred to as "standalone" IEs and have included versions 3 through 7.

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.

It is also possible to install Internet Explorer via Wine.

After Internet Explorer 7 is installed, an Internet Explorer 6 executable is still available in C:\WINDOWS\ie7, hidden by default. Launching this executable provides the user with the older IE6 interface, however web pages are rendered using the IE7 engine. The IE6 engine can be re-enabled by placing a file named "iexplore.exe.local" into the IE7 folder.

As an alternative to using IE standalone, Microsoft now makes available Microsoft Virtual PC images containing pre-activated copies of Windows XP with either IE 6 or IE 7 installed.[107] 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.[108][109]

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 court 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, or have unexpected behaviors. 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.[110] Microsoft does not allow the dependencies to be removed through this process, but the Internet Explorer executable (iexplore.exe) is removed without harming any other Windows components.