Microsoft provides a number of security-related resources.
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M I C R O S O F T I R E S O U R C E S
Windows security - Microsoft:
http://www.microsoft.com/protect/default.mspx
(patches)
http://update.microsoft.com/microsoftupdate/v6/default.aspx?ln=en-us
Security resources for home computer users
http://www.microsoft.com/security/default.mspx
A variety of resources including virtual labs and training materials
http://www.microsoft.com/technet/security/understanding/default.mspx
A round-up of worldwide Microsoft security sites
http://www.microsoft.com/security/worldwide.mspx
The Trustworthy Computing Initiative security overview
http://www.microsoft.com/mscorp/twc/security/overview.mspx
Microsoft security bulletin search
http://www.microsoft.com/technet/security/current.aspx
The Microsoft TechNet blog