Opera before 11.00 does not properly constrain dialogs to appear on top of rendered documents, which makes it easier for remote attackers to trick users into interacting with a crafted web site that spoofs the (1) security information dialog or (2) download dialog.
http://www.opera.com/support/kb/view/977/
http://www.opera.com/docs/changelogs/windows/1100/
http://www.opera.com/docs/changelogs/unix/1100/
http://www.opera.com/docs/changelogs/mac/1100/
http://secunia.com/advisories/42653
http://lists.opensuse.org/opensuse-security-announce/2010-12/msg00006.html