Microsoft Windows AntiSpyware
Microsoft Windows AntiSpyware (Beta) is a security technology that helps
protect Windows users from spyware and other potentially unwanted
software. Known spyware on your PC can be detected and removed. This
helps reduce negative effects caused by spyware, including slow PC
performance, annoying pop-up ads, unwanted changes to Internet
settings, and unauthorized use of your private information. Continuous
protection improves Internet browsing safety by guarding more than 50
ways spyware can enter your PC. Participants in the worldwide SpyNet™
community play a key role in determining which suspicious programs are
classified as spyware. Microsoft researchers quickly develop methods to
counteract these threats, and updates are automatically downloaded to
your PC so you stay up to date.
http://www.microsoft.com/athome/security/spyware/software/about.mspx
This is a Beta (test) version and as such is unsupported by Microsoft.