Gike Lee said..
You can use "ThreatFire AntiVirus" to protect your PC against viruses, rootkits, buffer overflows, and malware.
ThreatFire is unlike traditional antivirus products that rely on old fashioned "signature" technology and require updating every time a new threat occurs. ThreatFire's patent-pending ActiveDefense technology provides powerful protection against zero-day and emerging threats. It constantly monitors for both known and unknown viruses, worms, trojans, rootkits, buffer overflows, spyware, adware and other malware. It uses behavioral analysis to hunt down and paralyze threats that are too new or too clever to be recognized by traditional "signature-based" antivirus software. ThreatFire is the perfect complement to traditional antivirus programs.
It is free and available for Windows 2000/XP/Vista.