REDMOND, Washington (AP) -- Microsoft Corp. is giving its Web browser software its first major upgrade in years, amid signs that Internet Explorer's market share is eroding.

The release late Wednesday brings Microsoft's browser more in line with competing products such as Opera Software ASA's Opera and Mozilla Corp.'s Firefox. Internet Explorer 7, or IE7, adds features such as tabbed browsing, which lets people open several Web pages without cluttering their desktop with multiple open browser windows.

Microsoft has been heavily testing the new browser, releasing five beta versions over 14 months, and has periodically offered security updates for IE6, first released in 2001.

Still, a lag of more than five years between official releases has cost the company. Web analysis company WebSideStory estimates that Internet Explorer's U.S. market share is about 86 percent, while Firefox commands about 11 percent of the market and smaller offerings account for the rest. Two years ago, IE had about a 93 percent share.

Dean Hachamovitch, Microsoft's general manager for Internet Explorer, acknowledged the company could have done more sooner, but he said the new version should address users' concerns.

"We did have active development," he said. "The question is whether it was enough."

Matt Rosoff, analyst with independent researchers Directions on Microsoft, said Internet Explorer is important to Microsoft's business because most people believe an operating system should include a way to immediately access the Web.

Still, he said, Microsoft may not have seen much reason to spend a lot of money upgrading sooner since most people continued to use the older version.

Rosoff said the new product includes enough improvements to lure back some users.

But Colin Teubner, an analyst with Forrester Research, said people already using Firefox and rival products might not immediately come back. That's partly because those users have soured on Microsoft, he said, and partly because IE7 doesn't break much new ground.

"A year ago Firefox was head and shoulders above Microsoft's current offering, and I think even with IE7 it's mostly playing catch up," Teubner said.

But he does recommend that IE6 users upgrade, and he believes Microsoft may surpass competitors with future improvements.

Besides tabbed browsing, Microsoft has improved security to help keep users from falling victim to things like malicious software attacks and phishing scams. Microsoft products are a near-constant target of Internet attackers, and some people have recommended switching browsers because a less high-profile product might be more secure.

The Redmond software maker also has added a box in the browser that lets people search the Internet without going to a separate Web page, much like competitors.

In a last-minute change, people who are upgrading from the previous version of the browser will now have a clearer way to choose whether they want to use Microsoft's search engine or a competing one from companies like Google Inc. or Yahoo Inc. The change announced Friday was one of several aimed at soothing antitrust worries in Europe, where Microsoft faces a longrunning regulatory battle.

Microsoft is offering IE7 as a free download. Next month, the company also will begin delivering it to Windows XP users who have signed up to automatically receive security fixes. Hachamovitch said that's because the product makes major security improvements.

Such distribution also will provide a powerful tool in countering competition from rival browsers.

Security updates typically download with little or no user intervention, but with IE7 people will get an extra opportunity to elect not to upgrade. Also, even people using automatic updates will have to agree to let Microsoft check whether their copy of Windows is pirated before they can get IE7.

Microsoft expects that it will take months to gradually release IE7 automatically. The browser also will be an integral part of Microsoft's new operating system, Windows Vista, due out for big businesses in November and for consumers in January.