Microsoft have issued an out-of-band update at
http://support.microsoft.com/kb/2718704 entitled "Unauthorized digital certificates could allow spoofing".
Out-of-band updates such as these should be applied as soon as possible.
There is more on this at
http://technet.microsoft.com/en-us/security/advisory/2718704I applied the update via Windows Update and no re-boot was required.