Free AntiVirus
AVG Windows XP, Vista and Windows 7
Avast! Home Edition Windows XP, Vista and Windows 7
Avira AntiVir Personal Windows XP, Vista and Windows 7
Rising Windows XP, Vista and Windows 7
Microsoft Security Essentials Windows XP, Vista and Windows 7
Online Virus Scanners
Eset
Housecall
Kaspersky
Panda Active Scan
Free Firewalls
Online Armour Windows XP and Vista
Outpost Windows 2K, XP and Vista
Zone Alarm Windows 2K, XP, Vista and Windows 7 (check system requirements before downloading to make sure you have the appropriate service packs installed)
Spyware Prevention
SpywareBlaster
(updated 17th September, 2009)