article [news.com.com] Windows Defender" and is getting a new look as well as capabilities to detect rootkits, keystroke loggers and other threats. ... The updated application will be part of Vista, the successor to the Windows XP operating system that is expected to launch by the end of next year. Microsoft will also release Windows Defender for XP users. It will be released as an update to the current edition of Windows AntiSpyware
The Windows AntiSpyware application has performed quite well on my systems. It tends to rank quite highly in consumer level anti-spyware software comparisons. This new update could make this product a real market leader.
Leosghost is right about the Registry Monitor software though. I've got it on every machine I own and it catches way more than I thought it would. Now, with a parallel install of MS AntiSpyware and RegMon there are very few things that both products don't pop up warnings for. This wasn't the case about a year or so ago when RegMon caught a lot more. However, the quality of the MS product is impressive and getting better. It does a lot more that the other free spyware utilities do, that's for sure.