WASHINGTON (AP) - Microsoft Corp. disclosed plans Thursday to offer frustrated users of its Windows software new tools within 30 days to remove spyware programs secretly running on computers. But it might cost extra in coming months. In a shift from past practice, the world's largest software manufacturer said it may charge consumers for future versions of the new protective technology, which Microsoft acquired by buying a small New York software firm. Terms of the sale of Giant Company Software Inc. weren't disclosed. Spyware is a category of irritating programs that secretly monitor the online activities of Internet users and can cause sluggish computer performance or popup ads. Microsoft, whose Windows operating systems have often been criticized for lax security, traditionally has given consumers - at no charge - separate programs to improve security. It also has increasingly built other protective tools, such as firewall software, into Windows to repel hackers. The company's upcoming tool, available for its Windows XP and Windows 2000 software, will sweep for spyware and offer to remove suspicious programs. It also will continuously protect a computer against new spyware threats, said Mike Nash, vice-president of Microsoft's security business unit. Rival anti-spyware tools, such as Lavasoft Inc.'s popular "Ad-Aware" product, offer similar functions and many are free. Microsoft's tool, expected to be available within 30 days, initially will be free but the company isn't ruling out charging for future versions. "We're going to be working through the issue of pricing and licensing," Nash said. "We'll come up with a plan and roll that out." The security efforts, which cost hundreds of millions of dollars, are aimed at promoting consumer confidence in its flagship Windows products - which generated nearly $3 billion US in revenues this year. They also help attract new customers worried about growing threats from viruses, hacker attacks, spam e-mails and spyware. "Because Microsoft has a near monopoly, they don't have anybody to compete against. Giving away free stuff is a side effect of being a monopoly, whether they like it or not," said Daniel Geer, a prominent security expert and one of the company's most vocal critics. Microsoft's disclosure that it may eventually charge extra for Windows protection reflects a recognition inside the company that it could collect significant profits by helping to protect its customers. Some experts blame Microsoft for Windows vulnerabilities that help spread spyware. Microsoft and some others, meanwhile, said blame should be directed instead at spyware manufacturers. "Spyware usually gets on your computer through human error," said Marc Maiffret of eEye Digital Security Inc., which regularly discovers serious Windows flaws. Alan Paller, research director for the SANS Institute in Bethesda, Md., a computer-security organization, compared Microsoft's new anti-spyware tool to sophisticated products sold to help manage computer networks. "It's not just a clean-up-our-mess tool," said Paller.