I can't find anything in my stats on these, so I don't know how they're originating or from whom.
Never mind stats: look at raw logs.
Either the visitors are coming from your site or they're not. If they're not, it is not your problem and the advertiser can do whatever they normally do with a forged referer. If they ARE coming from your site, you can then research more deeply-- but don't bother about this part until you're sure they started out with you.