There has been a lot of alerts/news out today from several vendors about a new critical vulnerability just announced. 

Please note, many vendors are focusing on the fact that Windows 2000 and Windows XP is affected. 

HOWEVER, it is deeper than that; all Microsoft operating systems are affected.   The article only goes back to Windows 2000 but also covers XP, Vista, Windows Server 2003 and Server 2008.  There is an off-cycle patch from Microsoft already out (usually it’s once per month).  You can get this (and any others you may have missed) by clicking on Start - Windows Update.

http://www.microsoft.com/technet/security/Bulletin/MS08-067.mspx

Even if you have followed the proper best practices for segregation of your network and proper firewall proceedures I HIGHLY recommend getting this patch installed as soon as possible.