I ran Belarc Advisor the other day to verify that my computer is indeed a piece of cr_p (PC Pitstop was right) but in doing so I noticed it has a very helpful feature. It indicated that Windows Update KB902400 was corrupted. Microsoft Help basically said to rerun Windows Update but it showed KB902400 was already installed. I was kind of wary of uninstalling the update so I finally found the manual update site and reloaded it from there.
Since KB902400 is designated as a critical high priority update I was glad Belarc flagged it or I would have probably never known it was corrupted. I used to use Microsoft's MBSA program to verify updates but it was causing anti-virus scans to take forever so I removed it.
Belarc Advisor is a great freeware app IMHO.