Microsoft Security Essentials released yesterday.  Microsoft Security Essentials is a free* download from Microsoft that is simple to install, easy to use, and always kept up to date so you can be assured your PC is protected by the latest technology.  Those of you who have been paying to use OneCare can now get a free subscription to Security Essentials

I have been using the beta on my daughters laptop for a while and it has stopped several malware attacks. 

Download a free copy here:
http://www.microsoft.com/SECURITY_ESSENTIALS/