well the scripts should not have changed at all.
It could also be a post that inserted a malicious script.
Upgrading will help for sure.
But if you were hacked, it would be prudent to do the first step I suggested.
the newer version will block future attempts.
But it does not clean up any prior hacks.
It is also a good idea to change all passwords including the mysql user password.
Including any user passwords that have cp access or can post using html.
Have you tried to access the ubb cp directly.
Like:
http://www.mysite.com/forums/admin/login.php
