spamer help needed

[Outbackmark]

This is more than just a spammer, for that to happen something has been done to one or more of your php files.
I would suggest you upoad new newreply.php and newthread.php as I can't think how this could happen without those files having been changed. I stand to be corrected, but it would not hurt to do this, before you upload the new files, change the name of the old ones, just put a .old on the end so you can edit and reuse them if needed.
You should also change passwords to the CPanel and other FTP accounts, also run the VB Diagnostics/Suspect File Versions to ensure there are no other files that should not be there.