The Login Window in Apple Mac OS X 10.4 through 10.4.9 displays the software update window beneath the loginwindow authentication dialog in certain circumstances related to running scheduled tasks, which allows local users to bypass authentication controls.
http://www.vupen.com/english/advisories/2007/1470
http://www.us-cert.gov/cas/techalerts/TA07-109A.html
http://www.securitytracker.com/id?1017939
http://www.securityfocus.com/bid/23569
http://secunia.com/advisories/24966
http://lists.apple.com/archives/Security-announce/2007/Apr/msg00001.html