Perhaps you should turn off any registration & communication features from the old forum to avoid it sending out spam like this?
PS. Yes, there's a typo, registered as 'freeganer' by mistake.
New private message has arrived
From: firstname.lastname@example.org <email@example.com> Thu, Aug 25, 2011 at 7:15 PM
To: freeganer <firstname.lastname@example.org>
You have received a new private message from "kockhanass" to your account
on "Thunder&Lightning Forum" with the following subject:
You can view your new message by clicking on the following link:
http://forum.tnlgame.net/phpBB3/ucp.php ... lder=inbox
You have requested that you be notified on this event, remember that you
can always choose not to be notified of new messages by changing the
appropriate setting in your profile.
Thanks, Jonas (developer of Thunder&Lightning)