source: http://www.securityfocus.com/bid/20832/info

Sun Java System Messenger Express is prone to a cross-site scripting vulnerability because the application fails to properly sanitize user-supplied input. 

An attacker may leverage this issue to have arbitrary script code execute in the browser of an unsuspecting user in the context of the affected site. This may help the attacker steal cookie-based authentication credentials and launch other attacks.

Specific information regarding affected versions of Sun Java System Messenger Express is not currently available; this BID will be updated as more information is disclosed.

http://www.example.com/?user=&error=%3Cscript%3Ealert('hakin9');%3C/script%3E</a>