Microsoft says it can find no evidence that its security updates were causing serious problems in Windows 7 computers, and is pointing at malware as a potential culprit.
There were reports last week after UK security firm Prevx said users were seeing the 'black screen of death' - a completely blank screen after logging on - after applying security updates.
Prevx told BBC that it issued a fix that worked on some machines, but not on onther.
The company said system registry changes were the likely cause of the problems - but Microsoft denies that its system updates have modified permissions in the Windows registry.
Microsoft says that it has conducted a comprehensive review of its November updates.
"That investigation has shown that none of these updates make any changes to the permissions in the registry," said a blog entry from Microsoft's Security Response Centre.
"Thus, we don't believe the updates are related to the 'black screen' behaviour described in these reports.
"Because these reports were not brought to us directly, it's impossible to know conclusively what might be causing a 'black screen' in those limited instances where customers have seen it.
"However, we do know that 'black screen' behaviour is associated with some malware families such as Daonol."
Prevx spokesman David Kennerly blogged that users were reloading Windows to fix the problem, while offering its 'fix'.
"There can be many causes," he said, "But if your black screen woes began in the last two weeks after a Windows update or after running any security program (including Prevx) to remove malware during this time then this fix will have a high probability of working."
He said the company had identified ten or more problems that can trigger the dreaded black screen and that Windows 7, Vista, XP, NT and Windows 2000 are affected.
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