Internet Explorer

Windows Internet Explorer (formerly Microsoft 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 the second most widely used web browser, behind Google Chrome, which surpassed it in May 2012, attaining a peak of about 95% usage share during 2002 and 2003 with Internet Explorer 5 and Internet Explorer 6. Since its peak of popularity, its usage share has been declining in the face of renewed competition from other web browsers, and is 34.27% as of January 2012. It had been slightly higher, 43.55% as of February 2011, just prior to the release of the current version. 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 9, which is available as a free update for Windows 7, Windows Vista SP2, Windows Server 2008, and Windows Server 2008 R2. 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).

Versions of Internet Explorer for other operating systems have also been produced, including 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.

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.

Internet Explorer, using the Trident layout engine:

Supports HTML 4.01, CSS Level 1, 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.

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, but 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.

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 from Accuvant lab said Internet Explorer had a very big improve on security, Google Chrome and Internet Explorer had all 7 security function it should have. But Mozilla Firefox had only 3.