If you take a peek over at the National Vulnerability Database, we can see this article Here is the overview:
Buffer underflow in Microsoft Windows 2000 SP4, XP SP2 and SP3, Server 2003 SP1 and SP2, Vista Gold and SP1, and Server 2008 allows remote attackers to execute arbitrary code via a Server Message Block (SMB) request that contains a filename with a crafted length, aka "SMB Buffer Underflow Vulnerability."
This means this vulnerability could be exploited to create a worm. Further it means if one PC gets infected on your network, then quickly all of them will.
After doing some more research it seems there is already an exploit in the wild - it is set to "go off" during the Thanksgiving holiday here in the states.
Aw - that's okay Microsoft. I wasn't planning on getting any actual work done today.
Update Hey, Microsoft? I know you're busy and all but you do realize it does nobody any good for you guys to announce 'OMG you guys gotta update all of your systems right now' and then have your liveupdate site .. fail under the load?
Are you guys running IIS or something?