Yahoo's move comes amid increasing competition for Web surfers against rivals Google Inc. and Microsoft Corp., which also offer popular browser toolbars, in the market for search and information services, along with related advertising.

Anti-Spy for the Yahoo! Toolbar, which is being released as a beta, or test, version, allows users to identify potentially unwanted software that creeps into personal computers.

Spyware often monitors Web surfing habits and can also cause issues such as displaying advertising and redirecting users to a particular home page. Some spyware can creep onto PCs without a user's knowledge and others come attached to other programs.

Julie Herendeen, vice president of Yahoo's networking products, said that the anti-spyware features is the first offered by a major Web portal to a broad Internet audience for free.

"Spyware is a serious issue, Herendeen said, but did not give a date when the full release version of the toolbar with anti-spyware would be released.

After scanning a PC, a user has the option to disable, remove or keep spyware. Yahoo said its anti-spyware technology is based on Pest Patrol's software.

Yahoo's toolbar also features other tools such as a search window, a pop-up advertising blocker, bookmarks and other customizable features.