Microsoft has just released an advance notification of an out-of-band update to be released on 23rd of October. They will hold a special webcast on the 23rd at 10:00 am PT to discuss the release.

The information in the bulletin mentions a remote code exploit, but no fruther details are provided, however a restart will be required.

Microsoft rates the issue as critical for 2000/XP/2003 and important for vista/2008.