I'm guessing you read my thread that I posted yesterday of how I had this problem.
What he means to say Boofo is that its suppose to prevent hotlinking of your forums attachments or avatars from another site. If you hotlink an image attachment, every viewer who see's that attachment on that "other" site will come up on your forums as a guest, a very strange bug but I've had it happen to me.
I'll try this out later and see how it works