What is the patch for the KB958644 download black screen issue?

Microsoft has revealed a major security vulnerability and urgently released an important patch. This vulnerability could lead to widespread remote attacks and even complete system control; all Internet users are strongly advised to download this patch.

It has now been confirmed that there is a security issue which may be exploited by unauthenticated remote attackers to compromise the security of Microsoft Windows-based systems and gain control of these systems.