Microsoft's Security Bulletin Notification Service bulletins don't always coincide with the availability of security updates through Microsoft Software Update Services (SUS). Can I have my SUS server notify me when new Microsoft updates become available?
Your SUS server won't notify you about security updates, but Microsoft will if you subscribe to the SUS email notification service (http://www.microsoft.com/windows2000/ windowsupdate/sus/redir-email.asp). Occasionally, because of a backlog of email on the SUS notification service, you'll receive your email notification some time after the update is actually available.
—Randy Franklin Smith