Microsoft has unveiled two newly developed tools designed to combat spyware and viruses, both acquired as a result of takeovers.

The first beta of Windows AntiSpyware is now available for download from Microsoft's website here. It is built using software designed by spyware company Giant, which Microsoft acquired in December last year.

A crucial part of Windows AntiSpyware will be SpyNet, a network of PC users around the world that reports on spyware that needs to be blocked. The network was set up by Giant and Microsoft and is calling for members worldwide to join free of charge.

Microsoft will also release a tool that eliminates common viruses. It is designed to augment rather than replace traditional antivirus systems and is based on GeCAD technology, a Romanian antivirus company Microsoft bought in 2003.

The antivirus software will be available for download from 11 January and will be updated with fresh virus definitions on the second Tuesday of the month.

"Customers have told us that they need solutions that make it easier to keep computers protected from emerging and ever-changing threats," said Mike Nash, corporate vice president of the security business and technology unit at Microsoft.

"The solutions we're announcing today will offer customers additional resources to help protect their PCs against spyware and viruses on an ongoing and predictable basis."