Well, considering that the Operating system is Microsoft based, they know a lot about their systems and release fixes to vulnerabilities as and when they happen, Microsoft had OneCare which they pulled the plug on late last year (a very good bit of software and in my opinion a lot better than Norton) only thing you didnt get was the 5GB online storage.
BUT!!.. now they've come out with a FREE.. AV and Malware protection suite you can find it here
http://www.microsoft.com/security_essentials/[/QUOTE]