Microsoft has said it is looking into reports that its recent security updates are causing "black screen of death" problems.
After installing the updates, those users affected are left with a black desktop and little else.
British insecurity outfit Prevx was the first to notice the problem.
After logging on there is no desktop, task bar, system tray or sidebar. Instead users are left with a totally black screen and a single My Computer Explorer window, which might be minimised.
Prevx thinks that the problem can occur on a wide range of Windows machines from Windows NT through Windows 7.
It said there are lots of reasons that can cause black-screens to happen under Windows and not all of them are related to the security update.
Apparently it found at least 10 different scenarios that will trigger the same black screen conditions. Some of them have been hanging around for a few years waiting for the right upgrade to trigger them into inactivity.
It claimed most of the problems were caused by the way Windows handles registry keys.
Microsoft is taking this seriously and has issued a statement, though apparently it has no idea about how to fix the problem yet.
It is suggesting that customers "test and deploy" the November security updates.