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.
However, the latest patches appear to make some changes to those registry keys. The effect is that some installed applications aren't aware of the changes and don't run properly, causing a black screen, Morris said.