"Patch Tuesday" is the day each month that Microsoft releases their newest security updates, typically the second Tuesday of the month.  This month includes nine updates, including five marked "critical", and four rated as "important".  For a full breakdown, check out the Microsoft Security Bulletin posted on line. 

The critical patches impact Microsoft Windows, Office, and server software, so this affects just about everyone. 

A "critical" patch is defined by Microsoft as "a vulnerability whose exploitation could allow the propagation of an Internet worm without user action".  As a general rule, all critical patches should be installed as soon as possible. Note that many of the patches require a reboot for installation.  Also, if you have a managed service support plan with us, all patches are tested before installation.

Internet Explorer, which is typically patched every other month, will receive its third consecutive monthly patch this week.  For more general notes about the security patches, check out the post on ZDNet.