Moodle 1.9.16, 2.0.7, 2.1.4, and 2.2.1 were released today. The new versions include bug fixes and security fixes. Details of the security vulnerabilities will be released “approximately one week after” the new versions have been released.
Update (January 17, 2012): Moodle has now released information on the security issues fixed in the releases. Moodle 1.9.16 includes fixes for seven security vulnerabilities, including one for a serious vulnerability. Moodle 2.0.7 and 2.1.4 include fixes for eleven security vulnerabilities, including two for serious vulnerabilities. Moodle 2.2.1 includes fixes for ten security vulnerabilities, including two for serious vulnerabilities.