Microsoft has just published a remote vulnerability in the windows TCP/IP stack.

"This security update resolves several privately reported vulnerabilities in Transmission Control Protocol/Internet Protocol (TCP/IP) processing. The vulnerabilities could allow remote code execution if an attacker sent specially crafted TCP/IP packets over the network to a computer with a listening service. Firewall best practices and standard default firewall configurations can help protect networks from attacks that originate outside the enterprise perimeter. Best practices recommend that systems that are connected to the Internet have a minimal number of ports exposed."

Patch: http://update.microsoft.com/microsoftupdate
More info: http://www.microsoft.com/technet/security/Bulletin/MS09-048.mspx