In a not quite unprecedented move, Microsoft on Wednesday will release a critical security patch outside of its normal monthly schedule. This isn't the first time Microsoft has done this--the last time was in April 2007--but it is an unusual step for the software giant, which has highlighted its carefully-timed security releases as one of many benefits of the Windows platform.

While details of the patch are unavailable, it appears to concern a currently-unknown vulernability that affects several versions of Windows, including Windows 2000, XP, and Server 2003. Microsoft's latest Windows versions, Windows Vista and Server 2008, are also affected, but the vulnerability is rated as less severe on those systems.

Microsoft will ship at 10:00 am PT (1:00 ET) on Wednesday, Microsoft says. Users are advised to manually run Windows Update if they are not automatically prompted to download and install the patch.

You can find out more about this vulnerability on the Microsoft Web site.
http://www.microsoft.com/technet/security/Bulletin/MS08-oct.mspx