These are all tools that will help remove and prevent viruses and spyware / adware / malware from invading your computer. Download, install, and update all, if possible. NOTE: Uninstall Norton Anti-Virus, McAfee, eTrust Anti-Virus, or any other anti-virus program before installing AVG Anti-Virus or AVG Internet Security. You should only have one anti-virus program installed at a given time. More than one can cause extra performance loss and conflicts. Multiple anti-spyware, anti-malware, anti-adware programs can be installed at once safely.

Downloads

Microsoft Windows Update
http://update.microsoft.com

Windows Live OneCare Safety Scanner
http://safety.live.com

Grisoft AVG Anti-Virus Free Edition 8.0 ( Now with anti-spyware )
http://free.grisoft.com/doc/download-free-anti-virus/us/

Lavasoft Ad-Aware 2008
http://www.lavasoft.com/download_and_buy/product_comparison_chart.php

Microsoft Windows Defender
http://www.microsoft.com/athome/security/spyware/software

SpyBot: Search & Destroy 1.6.0
http://www.safer-networking.org/en/download