Internet Explorer


Internet Explorer (formerly Microsoft Internet Explorer and Windows Internet Explorer, (from August 16, 1995 to March 30, 2021) commonly abbreviated IE or MSIE) is a discontinued series of s developed by and included in the line of s, starting in 1995. It was first released as part of the add-on package that year. Later versions were available as free downloads, or in-s, and included in the (OEM) service releases of Windows 95 and later versions of Windows. New feature development for the browser was discontinued in 2016 in favor of new browser . Since Internet Explorer is a Windows component and is included in long-term lifecycle versions of Windows such as , it will continue to receive security updates until at least 2029. ended support for Internet Explorer on August 17, 2021, and ended support for IE on November 30, 2020. Internet Explorer will be discontinued on June 15, 2022, after which the alternative will be with IE mode for legacy sites. Internet Explorer was once the most widely used web browser, attaining a peak of about 95% by 2003. This came after Microsoft used to win the against , which was the dominant browser in the 1990s. Its usage share has since declined with the launch of (2004) and (2008), and with the growing popularity of mobile operating systems such as and that do not support Internet Explorer. Estimates for Internet Explorer's market share in 2021 , or by 's numbers ranked 9th. On traditional PCs, the only platform on which it has ever had significant share, it is ranked 6th at 1.15%, after . , IE's successor, first overtook Internet Explorer in terms of market share in November 2019. Microsoft spent over per year on Internet Explorer in the late 1990s, with over 1,000 people involved in the project by 1999. Versions of Internet Explorer for other operating systems have also been produced, including an version called Internet Explorer for Xbox and for platforms Microsoft no longer supports: and ( and ), and an embedded OEM version called Pocket Internet Explorer, later rebranded made for , , and, previously, based on Internet Explorer 7, for . On March 17, 2015, announced that would replace Internet Explorer as the default browser on "for certain versions of ". This makes the last release. Internet Explorer, however, remains on Windows 10 LTSC and primarily for enterprise purposes. Since January 12, 2016, only Internet Explorer 11 has official support for consumers; extended support for Internet Explorer 10 ended on January 31, 2020. Support varies based on the operating system's technical capabilities and its support life cycle. On May 20, 2021, it was announced that full support for Internet Explorer would be discontinued on June 15, 2022, after which, the alternative will be with IE mode for legacy sites. Microsoft is committed to support Internet Explorer that way to 2029 at least, with a one-year notice before it is discontinued. The IE mode "uses the engine", i.e. the code of Internet Explorer. The browser has been scrutinized throughout its development for use of third-party technology (such as the of , used without royalty in early versions) and security and privacy , and and that integration of Internet Explorer with Windows has been to the detriment of fair browser competition.


Internet Explorer 1

The Internet Explorer project was started in the summer of 1994 by , who, according to the Review of 2003, used source code from Mosaic, which was an early commercial web browser with formal ties to the pioneering (NCSA) browser. In late 1994, licensed Spyglass Mosaic for a quarterly fee plus a percentage of Microsoft's non-Windows revenues for the software. Although bearing a name like NCSA Mosaic, Spyglass Mosaic had used the NCSA Mosaic source code sparingly. The first version, dubbed Microsoft Internet Explorer, was installed as part of the ''Internet Jumpstart Kit'' in the pack for . The Internet Explorer team began with about six people in early development. Internet Explorer 1.5 was released several months later for and added support for basic table rendering. By including it free of charge with their , they did not have to pay royalties to Spyglass Inc, resulting in a lawsuit and a 8 million settlement on January 22, 1997. Microsoft was sued by Synet Inc. in 1996, for , claiming it owned the rights to the name "Internet Explorer".

Internet Explorer 2–10

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Internet Explorer 11

Internet Explorer 11 is featured in , which was released on October 17, 2013. It includes an incomplete mechanism for syncing tabs. It is a major update to its , enhanced scaling for high DPI screens, prerender and prefetch, decoding, , HTML5 full screen, and is the first Internet Explorer to support and Google's protocol (starting at v3). This version of IE has features dedicated to Windows 8.1, including cryptography (WebCrypto), () and . Internet Explorer 11 was made available for users to download on November 7, 2013, with in the following weeks. Internet Explorer 11's string now identifies the agent as "" (the underlying browser engine) instead of "MSIE". It also announces compatibility with (the browser engine of ). Microsoft claimed that Internet Explorer 11, running the SunSpider Benchmark, was the fastest browser as of October 15, 2013. Internet Explorer 11 was made available for and in the spring of 2019.

End of life

, officially unveiled on January 21, 2015, has replaced Internet Explorer as the default browser on . Internet Explorer is still installed in Windows 10 to maintain compatibility with older websites and sites that require and other Microsoft legacy web technologies. According to Microsoft, the development of new features for Internet Explorer has ceased. However, it will continue to be as part of the support policy for the versions of Windows with which it is included. On June 1, 2020, the removed the latest version of Internet Explorer from its list of supported browsers, citing its dated infrastructure that makes it hard to work with, following the suggestion of Microsoft Chief of Security Chris Jackson that users not use it as their default browser, but to use it only for websites that require it. Since November 30, 2020, the web version of can no longer be accessed using Internet Explorer 11, followed by the remaining Microsoft 365 applications since August 17, 2021. The browser itself will continue to be supported for the lifecycle of the Windows version on which it is installed until June 15, 2022. Microsoft recommends Internet Explorer users migrate to Edge and use the built-in "Internet Explorer mode" which enables support for legacy internet applications.


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

Standards support

Internet Explorer, using the MSHTML (Trident) : * Supports 4.01, parts of , Level 1, Level 2, and Level 3, 1.0, and Level 1, with minor implementation gaps. * Fully supports 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 . Support for 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 MSHTML browser engine in Internet Explorer 9 in 2011, scored highest in the official W3C conformance test suite for CSS 2.1 of all major browsers. * Supports in Internet Explorer 9 (MSHTML Trident version 5.0). Prior versions can render XHTML documents authored with HTML compatibility principles and served with a text/html . * Supports a subset of in Internet Explorer 9 (MSHTML Trident version 5.0), excluding SMIL, SVG fonts and filters. Internet Explorer uses to choose between standards mode and a "" in which it deliberately mimics 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 called . Internet Explorer was criticized by for its limited support for SVG, which is promoted by .

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 several 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 several extensions to the DOM that have been adopted by other browsers. These include the inner HTML property, which provides access to the HTML string within an element, which was part of IE 5 and was standardized as part of HTML 5 roughly 15 years later after all other browsers implemented it for compatibility, the XMLHttpRequest object, which allows the sending of HTTP request and receiving of HTTP response, and may be used to perform , and the designMode attribute of the content Document 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 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), profile, which adds timing and media synchronization support to HTML documents (similar to the W3C ), and the file format. However, all were rejected, at least in their original forms; VML was subsequently combined with (proposed by and ), resulting in the W3C-approved SVG format, one of the few vector image formats being used on the web, which IE did not support until version 9. 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 and page transitions, which are not found in W3C CSS, support for script code, in particular , as well as support for fonts in .


Support for s was first added in Internet Explorer 5. Internet Explorer supports favicons in , static and formats. In Windows Vista and later, Internet Explorer can display native Windows icons that have embedded PNG files.

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 Windows Explorer. Internet Explorer 5 and 6 had a side bar for web searches, enabling jumps through pages from results listed in the side bar. and were added respectively in Internet Explorer 6 and Internet Explorer 7. Tabbed browsing can also be added to older versions by installing or .


Internet Explorer caches visited content in the folder to allow quicker access (or offline access) to previously visited pages. The content is indexed in a database file, known as . Multiple Index.dat files exist which index different content—visited content, s, visited s, 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 . Administrators of s (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 behavior and others. Policy settings can be configured for each user and for each machine. Internet Explorer also supports .


Internet Explorer uses a architecture built on the (COM) technology. It consists of several major components, each of which is contained in a separate (DLL) and exposes a set of COM hosted by the Internet Explorer main executable, : * is the protocol handler for , , and . It handles all network communication over these protocols. * is responsible for MIME-type handling and download of web content, and provides a thread-safe wrapper around WinInet.dll and other protocol implementations. * houses the (Trident) introduced in Internet Explorer 4, which is responsible for displaying the pages on-screen and handling the (DOM) 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 s for runtime inspection and modification of the DOM tree. The DOM tree is further processed by a browser engine which then renders the internal representation on screen. * contains the user interface and window of IE in Internet Explorer 7 and above. * provides the navigation, local caching and history functionalities for the browser. * is responsible for rendering the browser user interface such as menus and toolbars. Internet Explorer does not include any native scripting functionality. Rather, exposes an API that permits 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 engine, which is a part of and allows any language implemented as an Active Scripting module to be used for client-side scripting. By default, only the JScript and modules are provided; third party implementations like (for ECMAScript 4 support) can also be used. Microsoft also makes available the runtime that allows , including -based dynamic languages like and , to be used for client-side scripting. Internet Explorer 8 introduced 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 , each tab process can host multiple web sites. The processes use asynchronous to synchronize themselves. Generally, there will be a single frame process for all web sites. In 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.


Internet Explorer exposes a set of Component Object Model (COM) interfaces that allows to extend the functionality of the browser. Extensibility is divided into two types: Browser extensibility and content extensibility. Browser extensibility involves adding entries, toolbars, menu items or (BHO). BHOs are used to extend the feature set of the browser, whereas the other extensibility options are used to expose that feature in the user interface. Content extensibility adds support for non-native content formats. It allows Internet Explorer to handle new s and new , e.g. or SPDY. In addition, web pages can integrate known as ActiveX controls which run on Windows only but have vast potentials to extend the content capabilities; and Microsoft Silverlight are examples. Add-ons can be installed either locally, or directly by a web site. Since malicious add-ons can compromise the security of a system, Internet Explorer implements several safeguards. Internet Explorer 6 with Service Pack 2 and later feature an Add-on Manager for enabling or disabling individual add-ons, complemented by a "No Add-Ons" mode. , Internet Explorer and its BHOs run with restricted and are isolated from the rest of the system. 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. Windows 8 and Windows RT introduce a of Internet Explorer that is entirely sandboxed and does not run add-ons at all. In addition, Windows RT cannot download or install ActiveX controls at all; although existing ones bundled with Windows RT still run in the traditional version of Internet Explorer. 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 a computer program or create s.


Internet Explorer uses a zone-based 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 the accidental installation of malware. Internet Explorer 7 introduced the phishing filter, which restricts access to sites unless the user overrides the decision. With version 8, it also blocks access to sites known to host . 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 that are in Microsoft's mainstream support phase. On December 16, 2008, recommended users switch to rival browsers until an emergency 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. A fix for the issue was released the following day with the Security Update for Internet Explorer KB960714, on Microsoft Windows Update. In 2010, Germany's Federal Office for Information Security, known by its German initials, BSI, advised "temporary use of alternative browsers" because of a "critical security hole" in Microsoft's software that could allow hackers to remotely plant and run malicious code on Windows PCs. In 2011, a report by Accuvant, funded by Google, rated the security (based on sandboxing) of Internet Explorer worse than but better than . A 2017 browser security white paper comparing Google Chrome, Microsoft Edge, and by X41 D-Sec in 2017 came to similar conclusions, also based on sandboxing and support of legacy web technologies.

Security vulnerabilities

Internet Explorer has been subjected to many security vulnerabilities and concerns such that the volume of criticism for IE is unusually high. Much of the , , and es 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 to install themselves. This is known as a ".” 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 in 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 had been overstated and there were safeguards in place. In 2006, new techniques using found more than a hundred vulnerabilities in standard Microsoft ActiveX components. Security features introduced in Internet Explorer 7 mitigated some of these vulnerabilities. In 2008, Internet Explorer had a number of published security vulnerabilities. According to research done by security research firm , 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 previous year. According to an October 2010 report in ', researcher Chris Evans had detected a known security vulnerability which, then dating back to 2008, had not been fixed for at least six hundred days. Microsoft says that it had known about this vulnerability, but it was of exceptionally low severity as the victim web site must be configured in a peculiar way for this attack to be feasible at all. In December 2010, researchers were able to bypass the "Protected Mode" feature in Internet Explorer.

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 from on Windows XP and Server 2003, IE6 SP1 on Windows 2000 SP4, IE7 on Windows Vista, XP, Server 2008, and Server 2003, IE8 on Windows 7, Vista, XP, Server 2003, and Server 2008 (R2). The warned users against using Internet Explorer and recommended switching to an alternative web browser, due to the major security hole described above that was . The Australian and French Government issued a similar warning a few days later.

Major vulnerability across versions

On April 26, 2014, Microsoft issued a security advisory relating to (use-after-free vulnerability in Microsoft Internet Explorer 6 through 11), a vulnerability that could allow "remote code execution" in Internet Explorer versions 6 to 11. On April 28, 2014, the United States 's (US-CERT) released an advisory stating that the vulnerability could result in "the complete compromise" of an affected system. US-CERT recommended reviewing Microsoft's suggestions to mitigate an attack or using an alternate browser until the bug is fixed. The UK National Computer Emergency Response Team (CERT-UK) published an advisory announcing similar concerns and for users to take the additional step of ensuring their antivirus software is up to date. , a cyber security firm, confirmed that "the vulnerability crashes Internet Explorer on Windows XP". The vulnerability was resolved on May 1, 2014, with a security update.

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 in 1997, the adoption was greatly accelerated: from below 20% in 1996, to about 40% in 1998, and over 80% in 2000. This made Microsoft the winner in the infamous '' against Netscape. was the dominant browser during 1995 and until 1997, but rapidly lost share to IE starting in 1998, and eventually slipped behind in 1999. The integration of IE with Windows led to a lawsuit by , Netscape's owner, accusing Microsoft of unfair competition. The infamous case was eventually won by AOL but by then it was too late, as Internet Explorer had already become the dominant browser. Internet Explorer peaked during 2002 and 2003, with about 95% share. Its first notable competitor after beating Netscape was Firefox from , which itself was an offshoot from Netscape. Firefox 1.0 had surpassed Internet Explorer 5 in early 2005, with Firefox 1.0 at 8 percent market share. 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.Borland, John
Browser wars: High price, huge rewards
''ZDNet'', April 15, 2003. Accessed June 2, 2012.
According to Internet Explorer's market share fell below 50% in September 2010. In May 2012, Google Chrome overtook Internet Explorer as the most used browser worldwide, according to . In September 2021, usage share is low globally, while a bit higher in Africa, at 2.61%.

Industry adoption

s are also used by many s 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 several Internet Explorer shells, and several content-centric applications like also use Internet Explorer's web browsing module for viewing web pages within the applications.


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 ' case. One of Microsoft's arguments during the trial was that removing Internet Explorer from Windows may result in system instability. Indeed, programs that depend on libraries installed by IE, including Windows help and support system, fail to function without IE. Before Windows Vista, it was not possible to run without IE because the service used ActiveX technology, which no other web browser supports.

Impersonation by malware

The popularity of Internet Explorer has led to the appearance of malware abusing its name. On January 28, 2011, a fake Internet Explorer browser calling itself "Internet Explorer – Emergency Mode" appeared. It closely resembles the real Internet Explorer but has fewer buttons and no search bar. If a user attempts to launch any other browser such as Google Chrome, Mozilla Firefox, , , or the real Internet Explorer, this browser will be loaded instead. It also displays a fake error message, claiming that the computer is infected with malware and Internet Explorer has entered "Emergency Mode.” It blocks access to legitimate sites such as Google if the user tries to access them.

See also

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Further reading

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External links

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Internet Explorer Architecture
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