The chat functionality in Moodle 2.0.x before 2.0.5 and 2.1.x before 2.1.2 allows remote authenticated users to discover the name of any user via a beep operation.
https://bugzilla.redhat.com/show_bug.cgi?id=747444
http://moodle.org/mod/forum/discuss.php?d=188316
http://git.moodle.org/gw?p=moodle.git%3Ba=commit%3Bh=d0157d827bc254ba386a5e5b41b13be2698ee76e