Most web statistics show Internet Explorer to currently be the most used web browser on the market, although its default inclusion in Microsoft Windows - which has over 85% market share for personal computers - makes it unlikely that this has anything to do with user preferences, let alone whether it is the best browser.
Internet Explorer has been criticized for numerous security holes, such as its tight integration with the Windows operating system and its ActiveX technology, which allows websites to run arbitrary programs (such as viruses) on the user's computer. It has also been criticized for ignoring web standards. Microsoft has fixed many of these problems version to version however, many of the security vulnerabilities are still present.
The history of Internet Explorer begins in 1995 with the release of Windows 95, and was originally a separate product released a little while after 95's Release that also came pre-installed on new computers. Although simple when compared to other Early Internet explorer versions, it was for many people the first introduction to the world of the Internet. In less then 3 months, Microsoft would release Internet Explorer 2.0, it's first cross-platform Browser, which included increased capabilities and marked Internet Explorers first real fight for Dominance with Netscape, then the Dominant Web Browser.
A year later Microsoft launched Internet Explorer 3.0, which in 6 hours was downloaded by over 30,000 people and a million in a week. Mew features were included such as Email, a online address book, and the browser was able to Display Jpg and GIF Files, play MIDI sound files and stream Audio without a separate program and increased support for Web Designing. In October 1997, Internet Explorer 4.0 was released, and featured vastly increased web design capability, allowing pages to become more dynamic in style (such as the ability to drag items on the screen or display drop down lists).
In March of 1999, Internet Explorer 5.0 was released, and largely focused on increasing web design capability and personalization, such as apps for Economics or a Internet Radio. 2 years later with the release of Windows XP in 2001, Internet Explorer 6.0 came onto the scene with a focus on Internet Security and User Privacy, allowing a user to decide what amount of Privacy they wanted on the Internet. For many younger Readers, this will ussualy be the first Internet Browser they had experience with. However, since it's release the Browser has begun to show it's age, being one of the most insecure choices for internet browsing available, with even microsoft itself asking users to abandon it for newer versions.
5 years after the release of IE 6, Microsoft released Internet Explorer 7.0 which had a focus on both increased Security and personalization. Of note in the changes was the inclusion of Tabbed browsing, which allowed more then one internet page to be open in one browser, a feature popularized by other browsers such as Firefox Three years later, Internet Explorer 8.0 was released, again with improvements to Security and a focus on increasing Browsing speed.
The latest version of the software, Internet Explorer 9.0 was released in 2011 and builds on the previous versions Security ability and improving speed and look, while losing the ability to be used on a Windows XP or prior. It is designed for use by modern computers and includes increased customization and personalization features. 
Main Article: Browser Wars