source: http://www.securityfocus.com/bid/6811/info

The Opera browser for Win32 (and possibly other) systems is prone to a remotely exploitable buffer overflow condition. For security purposes, Opera will display a warning any time a user of the client visits a link containing a username as part of the URI. An excessively long username will trigger a buffer overflow condition related to this security feature that may overwrite the stack frame of the affected function. Attackers may exploit this vulnerability to execute instructions on client systems. 

https://github.com/offensive-security/exploit-database-bin-sploits/raw/master/bin-sploits/22239.tgz