Microsoft has just published MS09-001 . This update addresses an SMB flaw.

"Vulnerabilities in SMB Could Allow Remote Code Execution (958687) This security update resolves several privately reported vulnerabilities in Microsoft Server Message Block (SMB) Protocol. The vulnerabilities could allow remote code execution on affected systems. An attacker who successfully exploited these vulnerabilities could install programs; view, change, or delete data; or create new accounts with full user rights. 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 URL: http://update.microsoft.com
Advisory Link: http://www.microsoft.com/technet/security/bulletin/ms09-jan.mspx