Opera 7.x and 8 before 8.01 does not clearly associate a Javascript dialog box with the web page that generated it, which allows remote attackers to spoof a dialog box from a trusted site and facilitates phishing attacks, aka the "Dialog Origin Spoofing Vulnerability."
http://secunia.com/secunia_research/2005-8/
http://secunia.com/multiple_browsers_dialog_origin_vulnerability_test/