Free Antivirus software roundup from LifeHacker : Here are three useful AV packages for Windows free to download and install for personal use: ClamWin - The only non-corporate of the bunch, ClamWin is free as in speech, and the lightest and the least intrusive option as well AVG Anti-Virus - Thorough scanner checks all your incoming and outgoing email, too Avast anti-virus - Slower but perhaps the most thorough for the worse-off machines.. be sure to schedule that scan to run overnight