I think it is all about the cookie "afscr" that is set in your browser. A user that simply visits a page that has an iframe from bigfish on the site get the afsrc-cookie set to the affiliate code from the visited page. So the visitor even dont need to download a game at this time - he can do it weeks or month later. the cookie is still in the browser. even if you download a game from a totaly different page than your first visit the owner of the page from the first visit gets this contact!