Microsoft has released a free trial copy of anti-spyware software it purchased last month.

It marks the company's entry into the fast-growing market for products that block surreptitious snooping programs, and has promised monthly releases of tools to stop new malicious software.

The company published Windows AntiSpyware (Beta) on its main website, 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.

It also promised to offer a new tool to remove malicious programs along with its monthly security updates for customers plagued by worms and viruses that target its Windows platform.

However, yesterday, the software giant delayed the release of its anti-spam and anti-virus improvements to the Exchange e-mail server, so it's not all full-speed ahead.

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 anti-spyware users created by Giant to help spot and block new spyware programs.

The software is only available to "genuine" Windows users - Microsoft asks visitors to validate their Windows license before obtaining a copy, 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 subscriptions to continue using that product, which runs on more versions of Windows and has features that are not in the beta release. Giant AntiSpyware users who want to install and use Microsoft's version need to uninstall the Giant product first, Microsoft said.