UPDATE
From the BBC Website -
Malware has been blamed for a problem with the Windows 7 operating system, dubbed the 'Black Screen of Death'.
Some Windows users are confronted by a totally black screen after they log on to their system.
Initially it was thought that Microsoft's own security update could have caused the problem but that has now been ruled out.
The software firm that suggested the security update was the problem has apologised for its claims.
Reports suggest the problem also affects Windows Vista and XP.
In a blog posting on its security site, Microsoft said that it had investigated the claims and "found that our November Security Updates are not making changes to the system that these reports say are responsible for these issues".
The firm said that the behaviour was associated with malware, such as Daonol, and that this was probably the root cause.
Software firm Prevx, who had said the November update may have been to blame, have since retracted their statement, saying it had been a "challenging issue" to identify the cause.
"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," the firm wrote on its website.
"Since more specifically narrowing down the cause we have been able to exonerate these patches from being a contributory factor."
Prevx apologised to Microsoft for "for any inconvenience" its earlier claims may have caused.
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