Microsoft has finally released to the public their new AV tool which has been in beta for months.
http://www.microsoft.com/security_essentials/
If you have an updated AV purchased (and maintained in the past 9 months), this likely won't interest you. If you do not have an updated AV or you have another free AV (I used Grisoft's AVG for years), this is a good substitute. I have provided a review for your interest ...
http://arstechnica.com/microsoft/news/2009/09/first-look-microsoft-security-essentials-impresses.ars
As a side note, a guildie has their account jacked and this new version found it while others did not. It is important to keep your AV updated (daily or at least weekly).
http://www.microsoft.com/security_essentials/
If you have an updated AV purchased (and maintained in the past 9 months), this likely won't interest you. If you do not have an updated AV or you have another free AV (I used Grisoft's AVG for years), this is a good substitute. I have provided a review for your interest ...
http://arstechnica.com/microsoft/news/2009/09/first-look-microsoft-security-essentials-impresses.ars
As a side note, a guildie has their account jacked and this new version found it while others did not. It is important to keep your AV updated (daily or at least weekly).