Microsoft Thursday released a free trial copy of anti-spyware software it purchased last month, marking the company's entry into the fast-growing market for products that block surreptitious snooping programs, and promised monthly releases of tools to stop new malicious software.

The company published Windows AntiSpyware (Beta) on the Microsoft.com Web site, allowing Windows users to download and install a copy of the product, formerly known as Giant AntiSpyware, for free. The release makes good on a promise Microsoft made last month to quickly release a trial copy of the rebranded tool, after it purchased Giant Company Software of New York.

In a separate announcement, Microsoft promised to offer a new tool to remove malicious programs along with its monthly security updates, formalizing a program of releasing quick-fix tools for customers plagued by worms and viruses that target its Windows platform.

The company offered copies of the AntiSpyware beta on the Microsoft.com Web site, describing the product as a way to protect its Windows customers from spyware and other unwanted software that can slow PC performance or display unwanted pop-up ads.

The product is available to Windows 2000, XP and Windows Server 2003 users and requires a connection to the Internet to participate in SpyNet, the worldwide network of AntiSpyware users created by Giant to help spot and block new spyware programs.

According to the company's Web page, Windows AntiSpyware is only available to "genuine" Windows users running licensed copies of the operating system. Microsoft asked visitors to Microsoft.com to validate their Windows license before obtaining a copy of the Windows AntiSpyware beta, but allows downloads even if visitors have not certified that their copy of Windows is legal.

Microsoft asks existing users of Giant AntiSpyware with active anti-spyware subscriptions to continue using that product, which runs on more versions of Windows and has features that are not in the beta Windows AntiSpyware release. Giant AntiSpyware users who want to install and use Microsoft Windows AntiSpyware need to uninstall the Giant product first, Microsoft said on its Web page.

Some security experts object to Microsoft limiting security-focused updates for its products to licensed users, arguing that security threats that take advantage of shortcomings in the ubiquitous Windows operating system affect everyone.

The IDG News Service is a Network World affiliate.