Microsoft Updates - Critical Updates and Patches for Windows 2000, XP & Vista
Microsoft Security Essentials - Microsoft Security Essentials provides real-time protection for your home PC that guards against viruses, spyware, and other malicious software.
AVG FREE - Free Anti-Virus Proctection for your Computer
Trend Micro House Call - Free online scan of your computer for Viruses, Spyware and Malware