Today is outside Microsoft's typical update schedule. Yet, today they pushed out a patch for a security vulnerability that affects every version of windows, due to it being actively targeted.
http://www.microsoft.com/technet/security/bulletin/MS10-046.mspx The vulnerability deals with how Windows parses shortcuts. If you browse to a directory with a specially-crafted shortcut, it could cause code to be executed on your system.
It is STRONGLY suggested you install this update, if you don't have automatic updates enabled.