Opera before 10.63 allows remote attackers to cause a denial of service (application crash) via a Flash movie with a transparent Window Mode (aka wmode) property, which is not properly handled during navigation away from the containing HTML document.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A12263
http://www.opera.com/docs/changelogs/windows/1063/