Microsoft just released their "out of band" security bulletin. There is a gaping hole in the way most Microsoft platforms serve Remote Procedure Calls (RPC). This is on the order of severity of the original RPC DCOM vulnerability that led to the wide spread of the MSBlaster worm in August or 2003.
I have never understood why anyone does RPC over the Internet but I guess it is needed for OWA and other Microsoft propriatary applications/protocols. So, while blocking the relevent ports, 135, 443, and 593, might be a good idea, if those ports are open on your firewall it is probably because you need them and you will break something if you block it.
Get patched now.