Since this was the most critical patch, it is the one most likely to be applied to many different machines on various iterations of Windows. While vague at best, people are alluding to the patch causing machines to act strange:
Applying the MS07-040 patch for the .NET framework, which as luck would have it is probably Redmond's most important security fix this month, can lead to systems going "haywire", the SANS Institute's Internet Storm Centre reports.
This wouldn't be the first time this has happened. If there is an issue, we'll see a “patch for the patch”. The details are a little light, so hopefully we'll learn more soon.