gnome-screensaver 2.28.0 does not resume adherence to its activation settings after an inhibiting application becomes unavailable on the session bus, which allows physically proximate attackers to access an unattended workstation on which screen locking had been intended.
https://launchpad.net/bugs/411350
https://bugzilla.gnome.org/show_bug.cgi?id=600488
http://www.ubuntu.com/usn/USN-866-1
http://www.mandriva.com/security/advisories?name=MDVSA-2010:040