So, to add some more data to the case.. from this campaign I ran on WarOfClicks I received :
31476 non-unique hits
from
1067 different IP addresses,
at
23379 different moments in time
(which means that they were not delivered all at the same time which would mean absolute bot activity but that's not the case)
So, somehow, the site made ~1000 members do an average of 31 page loads on my site..
Digging a bit more I see that there are 100 different IP addresses that delivered from 100 up to 450 hits each on the ads page.
Maybe I should ask the admin for some explanation.. as that makes no sense in a PTC..