Microsoft has denied that Windows Updates are to blame for reports of so-called Black Screens of Death.

The problem was raised by British security firm Prevx, which claimed Windows Updates had invalidated several key registry entries, resulting in PCs booting with a black screen displaying only an Explorer window.

However, both Microsoft and Prevx claim that further investigations have exonerated the Windows Updates from blame.

We apologise to Microsoft for any inconvenience our blog may have caused - this has been a challenging issue to identify

"We’ve conducted a comprehensive review of the November Security Updates, the Windows Malicious Software Removal Tool, and the non-security updates we released through Windows Update in November," Microsoft claims in a statement on its Security Response Center blog.

"That investigation has shown that none of these updates make any changes to the permissions in the registry. Thus, we don’t believe the updates are related to the 'black screen' behaviour described in these reports."

Microsoft instead points the finger of blame at malware. "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 apology

Prevx has apologised for pinning the blame on Microsoft's patches. "Having narrowed down a specific trigger for this condition we've done quite a bit of testing and re-testing on the recent Windows patches including KB976098 and KB915597 as referred to in our previous blog," Prevx's Jacques Erasmus states on the Prevx blog. "Since more specifically narrowing down the cause we have been able to exonerate these patches from being a contributory factor."

"We apologise to Microsoft for any inconvenience our blog may have caused. This has been a challenging issue to identify. Users who have the black screen issue referred to can still safely use our free fix tool to restore their desktop icons and task bar."