Microsoft has recently announced several critical security update as detailed at http://www.microsoft.com/technet/security/bulletin.ms04-oct-mspx.

Two observations I'd like to offer. The time from annoucement of a vulnerability to the serious exploit of that vulnerability has decreased over time. Second, most the "big news" worms in the last few years have taken advantage of vulnerabilites for which fixes were available, but not applied. This makes it easy to predict that within 3 weeks, there will be some big time worm or other exploit hit the net that attempts to leverage one or more of these issues.

Stay tuned and stay patched.
-brett