It's not often that Microsoft breaks their update cycle to release a patch but when they do it's generally a good idea to get that patch installed or face infection.

Microsoft Security Bulletin MS08-067 released this morning outlines a vulnerability in the Server Service, of ALL Versions of Windows, that allows for remote code execution (RCE).
The bulletin says that the vulnerability was privately reported which at first lead me to believe that this was not being actively exploited or "in the wild" but other MS pages claim this is being exploited already.

Get patched people, this exploit is nasty.

Dave