Opera before 10.54 on Windows and Mac OS X, and before 10.60 on UNIX platforms, does not properly restrict certain uses of homograph characters in domain names, which makes it easier for remote attackers to spoof IDN domains via unspecified choices of characters.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A11603
http://www.vupen.com/english/advisories/2010/1673
http://www.vupen.com/english/advisories/2010/1529
http://www.securityfocus.com/bid/40973
http://www.opera.com/support/search/view/961/
http://www.opera.com/docs/changelogs/windows/1054/
http://www.opera.com/docs/changelogs/unix/1060/