Not all scam traffic is PPC (pay-per-click), the subject of another thread I wrote. In fact, many companies simply offer visitors, rather than some scheme where you bid for visitors. Nonetheless, the idea is the same. Trick the consumer into buying low quality traffic. Where does the low quality traffic that cheap PPC and cheap direct traffic companies come from? Well, the sources could be bots, visitors that aren't even human, and another source could be redirected domains.