From ISC:

We have received a report from Tyler that a vulnerability affecting Microsoft SMB2 can be remotely crashed with proof-of-concept code that has been published yesterday and a Metasploit module is out.

We have confirmed it affects Windows 7/Vista/Server 2008. The exploit needs no authentication, only file sharing enabled with one 1 packet to create a BSOD. We recommend filtering access to port TCP 445 with a firewall.
and interestingly,

Windows 2000/XP are NOT affected by this exploit.

I haven't put ** ** for greater attention required, since SMB (445) should be filtered on the firewall.