Microsoft Security Advisor

A comprehensive list of current and archived security-related issues with Microsoft products.

Links:
http://www.microsoft.com/security/default.asp
http://www.microsoft.com/security/bulletins/current.asp?

NTBugTraq

NTBugtraq is a mailing list for the discussion of security exploits and security bugs in Windows NT and its related applications.

Links:
http://ntbugtraq.ntadvice.com/

NTSecurity.net

A comprehensive list of security related news issues and latest vulnerabilities and exploits with Windows NT.

Links:
http://www.ntsecurity.net

SecurityFocus.Com

SecurityFocus.com is a single place, or community, on the Internet where people and corporations can go to find security information and have security questions answered by leading authorities in the industry. This site provides access to security links and resources including news, books, mailing lists, tools and products, and security services. In addition to this knowledge, SecurityFocus.com features one of the strongest collection of security advisories, vulnerabilities and solutions available on the Internet. Each of these resources may be customized for your needs via the "personalize" option on the home page.

Links:
http://www.securityfocus.com/
http://www.securityfocus.com/bid/