"Microsoft's latest round of security patches appears to be causing some PCs to seize up and display a black screen, rending the computer useless.

The problem affects Microsoft products including Windows 7, Vista and XP operating systems, said Mel Morris , the CEO and CTO for the U.K. security company Prevx.

Prevx was alerted to the problem by users of its security software last week, Morris said. Microsoft apparently made changes to the Access Control List (ACL), a list of permissions for a logged-on user. The ACL interacts with registry keys, creating visible desktop features such as a sidebar."