Microsoft has released an out-of-band critical update...

Microsoft has released an out-of-band update, designated MS14-068, to address a critical vulnerability in server versions of Windows, including Server Core.

The update is also being provided to desktop versions of Windows (including the Windows Technical Preview) for what Microsoft calls "...additional defense-in-depth hardening that does not fix any known vulnerability."

Please ensure that you run updates on your Windows computers, full details here.