If you had any problems on the last update Tuesday this may be why.
Microsoft pulls Patch Tuesday security fix

from the article:
"Tech giant Microsoft has recommended that an update released in the latest Patch Tuesday be removed, after users reported incidents of the "blue screen of death" after installation.

Microsoft released two critical security updates and others rated as "important" for Windows and Internet Explorer as part of its latest round of Patch Tuesday updates.

However, a number of Windows 7 users have reported issues with security update 2823324, which is part of security bulletin MS13-036.

MS13-036 was meant to fix three privately disclosed flaws and one publicly disclosed flaw in an NTFS kernel-mode driver related to the elevation of privileges when a user is logged in. However, once installed, security update 2823324 -- part of the bulletin -- may produce a "STOP: c000021a (Fatal System Error)" problem for users. The error occurs early in the startup process, and no Memory.dmp file is created.

As a result, Microsoft has temporarily pulled the patch from its security bulletin while the issue is being investigated.

Microsoft recommends that users uninstall the patch, and warns that another issue with the security update may cause anti-virus programs cease to work correctly. The Redmond giant says that Kaspersky Anti-Virus for Windows Workstations and Kaspersky Anti-Virus for Windows Servers versions 6.0.4.1424 and 6.0.4.1611 may display an error message stating that licenses for the products are not valid, and so the software will cease to function."