SEATTLE (Reuters) - Microsoft Corp. (Nasdaq:MSFT - news) released Internet Explorer 7 on Wednesday, the first major upgrade to its Web browser since 2001 with new features aimed at preventing online fraud and improving ease of use. Microsoft's IE remains the most widely-used software to surf the Web, but the long gap between major releases allowed for the emergence of the company's most formidable browser competitor since it vanquished the once-dominant Netscape. Mozilla Firefox, a free open-source browser, has steadily gained users since its introduction in 2004 with features such as an integrated search window to allow users to do a Web query without opening another page, tab browsing to toggle between different sites and a pop-up window blocker. These features are included in the new Internet Explorer and Microsoft also touted the security improvements to the browser including color-coded warnings in the address bar to indicate whether a Web site can be trusted. IE 7 is available immediately to Windows XP users and it will eventually serve as the default browser for Microsoft's much-anticipated Windows Vista operating system, due out to consumers in early 2007. According to analysts, consumers increasingly identify the quality of an operating system with the quality of its browser and that makes a well-received browser important for Microsoft -- even if it is not sold as a separate product. "How would it look if Microsoft didn't have a good browser as part of Windows? It wouldn't look good," said Forrester Research analyst Colin Teubner. Microsoft said it is already at work on the next version of Internet Explorer to ensure that long gaps between updates do not occur again. "Should we have done more, sooner, earlier? It's rare to not say that in hindsight," said Dean Hachamovitch, general manager of the Internet Explorer team at Microsoft. Internet Explorer registered an 86 percent global share in October, Mozilla Firefox 11.5 percent and both Apple Computer Inc.'s (Nasdaq:AAPL - news) Safari and Norway's Opera Software (OPERA.OL), less than 2 percent, according to OneStat.com. "It's exciting to see Microsoft reenter the browser space after leaving for five years," said Christopher Beard, vice president of products for Mozilla. "It's great to see that IE is adopting the features that we popularized." Mozilla said it also plans to release an upgraded browser, Firefox 2, within the next few weeks. The upgrade will include a feature to allow users to restore work done online if the browser or PC crashes, a spell check function for e-mails or blog postings and suggestions for search queries. Microsoft's Windows Live is the default search engine on Internet Explorer 7, but users will have the option to change to competing search engines. In Mozilla Firefox, the default search engine in the U.S. is Google Inc. (Nasdaq:GOOG - news) Competitors raised objections to Microsoft making its own search engine the default setting over concern that it would unfairly drive traffic to Windows Live, but analysts said consumers will eventually gravitate toward the search engine that produces the best results. The new browser will be sent as an automatic security update and then users will have an option to install the new Internet Explorer onto their PC. Companies also have the option to block its workers from installing the new browser. IE 7 is available for download at www.microsoft.com/ie.