Ubuntu Security Notice 537-2 – USN-537-1 fixed vulnerabilities in gnome-screensaver. The fixes were incomplete, and only reduced the scope of the vulnerability, without fully solving it. This update fixes related problems in compiz.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/60627/USN-537-2.txt
Source: https://packetstormsecurity.com/files/60627/Ubuntu-Security-Notice-537-2.html