Microsoft will release the latest version of Internet Explorer at noon Eastern time on Thursday, bringing major changes in a bid to hold onto the browser's dominance and fend off an increasingly crowded field of browsers, including the still-surging Mozilla Firefox.

Internet Explorer 8 brings to the table a number of new user-friendly features, increased standards support, and much improved security. The browser has been downloaded tens of millions of times since it entered public testing mode a little more than a year ago, constituting one of Microsoft's largest beta tests ever.

Improved security is one of IE8's most significant features. NSS Labs released an independent study early Thursday showing IE8 significantly besting Mozilla Firefox, Apple Safari, Google Chrome, and Opera in catching and blocking malware. With its SmartScreen filtering, IE8 Release Candidate 1 caught 69% of malware, while Firefox 3.07 caught only 30%.

In telemetry from beta testers, Microsoft has found malware to be a common occurrence -- one IE8 user in 40 has gotten a malware block, while 1 million users per month are prevented from browsing to phishing sites.

IE8 also contains a number of other security features, including an InPrivate Browsing mode that keeps no trail of browsing history and new features that prevent certain cross-site scripting attacks, click-jacking, and the installation of malicious ActiveX controls.

Nevertheless, a hacker successfully hijacked a machine running the IE8 release candidate and Windows 7 beta -- competitive browsers were hacked, too -- in a contest at the CanSecWest security conference on Wednesday.

The user interface in IE8 has been overhauled, adding new features such as color-coded browser tabs to group recently opened tabs together, the ability to recommend sites, a new visual search feature that allows users to see pictures of things such as eBay and Amazon results, auto-completion of searches and URLs, and a toolbar like Mozilla Firefox's for searching within a page. New tabs also show commonly visited Web sites as links, and tabs work in isolation so that if one tab crashes, the entire browser doesn't.

Throughout the testing process, Microsoft has focused most heavily on two new usability features, Web Slices and Accelerators. Accelerators let users perform actions like translation, mapping, and search from the right-click context menu, which brings up a window inside the current page to show translated text, a map, or search results.

Web Slices, which require work on the part of site developers and therefore are still few and far between, let users create a link on their favorites bar, which brings up only a small portion of a Web site, such as a condensed local weather forecast.

Microsoft claims that IE8 is faster or as fast as its main competitors, though the claim is debatable since Microsoft itself did the tests. The company released a high-speed video last week showing highly trafficked Web sites loading side by side in multiple browsers; IE8 came out ahead more often than not. Still, Microsoft isn't overplaying its hand here, simultaneously raising and downplaying the results. "These differences come down to milliseconds," Dean Hachamovitch, Microsoft's general manager of Internet Explorer, said in an interview.

The other significant -- and controversial -- new feature in IE8 is standards support. While developers and standards advocates have long complained that IE didn't support Web standards well enough, standards support comes at a cost, namely compatibility. In IE8, Microsoft includes both a legacy browsing mode and a standards browsing mode so that non-standard sites still load.

Developers can add a tag to their sites letting IE know if the sites should be opened in standards mode or compatibility mode. Microsoft also maintains a blacklist of standards-mode incompatible sites.

IE8 will be available at launch in 25 languages, for Windows XP, Windows Vista, and Windows Server in both 32-bit and 64-bit editions. However, IE8 won't be available for the Mac.

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