I really liked Microsoft's Windows Defender, and I was pleased to find out that they recently expanded it into a full (and free) AV suite: Security Essentials:

I really liked Microsoft's Windows Defender, and I was pleased to find out that they recently expanded it into a full (and free) AV suite: Security Essentials: http://www.microsoft.com/Security_Essentials/ http://www.microsoft.com/Security_Essentials/ It runs unobtrusively in the background (only a tray icon), is simple to use, and doesn't install additional cruft (e.g., the AVG IE toolbar).