Microsoft Windows Update   for O/S & Security Patches
Microsoft XP Powertoys   TweakUI & other OS Utilities

VIRUS INFORMATION CENTRES
BitDefender
        On-Line Scanner   Memory, Boot & Virus/Trojan scanning
Computer Associates
F-Secure
M^cAfee
Panda Software
        On-Line Scanner   On-line scanner
RAV Anti-Virus
        On-Line Scanner   On-line scanner
Sophos
Symantec AntiVirus Research Centre
        Hoax Pages   To debunk those rumours.....
        On-Line Scanner   Security path & Virus/Trojan scanning
        Virus Definitions   Pattern file downloads
        Virus Encyclopedia   Home page for All Viruses, listed alphabetically
Trend Virus Information Centre PC-cillin
        On-Line Scanner   Housecall Virus Scanning
Trojan Remover   Excellent anti-trojan tool
WindowSecurity . com
        On-Line Scanner   Highly rated Trojan scanner