A problematic security update in this month's Windows 7 Patch Tuesday has been pulled by Microsoft, when it was found that some computers failed to boot after applying it. Update 2823324 was supposed to fix a "moderate-level vulnerability," but instead it causes an error "when paired with certain third-party software." The update has since been pulled from the list of fixes so it can't cause any more problems. If you've downloaded the update, Microsoft recommends following the steps outlined here to get your system back up and running. Even if your system is still fully functional after the update, the folks in Redmond still recommend uninstalling it just in case. While it's unfortunate something like this happened, at least Microsoft is taking care of the problem.
Source: Ars Technica