The JavaScript implementation in WebKit allows remote attackers to send selected keystrokes to a form field in a hidden frame, instead of the intended form field in a visible frame, via certain calls to the focus method.
https://bugzilla.mozilla.org/show_bug.cgi?id=552255
http://www.vupen.com/english/advisories/2011/0212
http://www.securityfocus.com/archive/1/510070/100/0/threaded
http://secunia.com/advisories/43068
http://lists.opensuse.org/opensuse-security-announce/2011-01/msg00006.html