Early reports are suggesting problems after users apply one of the six patches issued by Microsoft on Tuesday.
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.
"The reports we got so far seem not to lead to any specific thing that happens in many cases, just various things going haywire," it said.
PCs in the UK office of one well-known component manufacturer are among those sent gaga by the update. Workers are having trouble managing their email and contacts after the security fix, according to sources at the firm.
Some of the problems involved with the update have been documented by Microsoft. Users are advised to review knowledge base articles that refer to the particular version of .NET and Windows they are running for more information, which are listed under the "known issues" section of the bulletin.
The SANS posting, and feedback we're hearing, suggests the problems some users are experiencing are more than these knowledge base articles might suggest but at least these postings provide a starting point for users before they refer outstanding issues they might still be having to Microsoft or their support partners. ®