The Installer application in Apple Mac OS X 10.4.8 and earlier, when used by a user with Admin credentials, does not authenticate the user before installing certain software requiring system privileges.
http://www.vupen.com/english/advisories/2006/4750
http://www.us-cert.gov/cas/techalerts/TA06-333A.html
http://www.securityfocus.com/bid/21335
http://securitytracker.com/id?1017304
http://secunia.com/advisories/23155
http://lists.apple.com/archives/security-announce/2006/Nov/msg00001.html