Today, Microsoft released its monthly Security Bulletin Summary, detailing the security patches it is releasing this month. There are two bulletins for Windows itself; both have a maximum severity rating of Critical. The first, MS10-042, affects Windows XP and Server 2003; the second, MS10-043, affects Windows 7 and Server 2008 R2. The first patch addresses the vulnerability in the Help and Support Center, which is currently being actively exploited.
There are also two bulletins for Microsoft Office and its components, with severity ratings of Critical and Important. All of the patches should be available via Windows Update, or by download links in the Security Bulletin Summary.
The SANS Internet Storm Center has published their usual summary and evaluation of these patches.
I recommend installing these patches as soon as you conveniently can.