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.