Ask HN: Is there fraud here? If not, what is the motivation?

http://www.zapbux.com/viewads.php

I own one of the site being targeted but don't buy crappy traffic through such services.

What possible motive could there be to driving free traffic to one of my sites? Interesting that many sites are within industries with CPCs would be quite high.

50k referrals since the start of April is not small. I cannot see a reason why anyone would do this.