A critical security threat was announced and an out of sequence patch released yesterday by Microsoft.
It affects ALL pcs running Vista, Windows7, 8, 8.1 and Windows RT.
There is specific news here if you want more http://www.cnet.com/news/microsoft-rushes-emergency-security-fix-for-versions-of-windows/
And the technical stuff is here https://technet.microsoft.com/library/security/MS15-078?f=255&MSPPError=-2147217396#ID0EKIAE
Please patch all your PCs and Servers immediately.