Virus alerts for Microsoft products at http://www.microsoft.com/technet/treeview/?url=/technet/security/virus/alerts/ .
Security Notification Service at http://register.microsoft.com/subscription/subscribeme.asp?ID=135 .
Use this service to register for regular e-mail bulletins that notify you of the availability of new fixes and updates.
CERT Advisory Mailing List at http://www.cert.org/contact_cert/certmaillist.html .
Informative advisories are sent when vulnerabilities are reported .
Windows and .NET Magazine Security UPDATE at http://email.winnetmag.com/winnetmag/winnetmag_prefctr.asp#Security .
This announces the latest security breaches and corresponding fixes. It also gives advice on reacting to vulnerabilities.
NTBugtraq at http://www.ntbugtraq.com/default.asp?pid=31&sid=1#020 .
This is an open discussion of Windows security bugs and exploits. Vulnerablities that do not have patches are discussed.
Internet Storm Center at http://isc.incidents.org .
This site tracks the frequency of worms, denial of service attacks, as well as other kinds of attacks.
Security Focus Web site at www.securityfocus.com .