Since the emergence of affiliate marketing, there has been little control over affiliate activity. Unscrupulous affiliates have used spam, false advertising, forced clicks (to get tracking cookies set on users' computers), adware, and other methods to drive traffic to their sponsors. Although many affiliate programs have terms of service that contain rules against spam, this marketing method has historically proven to attract abuse from spammers.
The terms of an affiliate marketing program are set by the company wanting to advertise. Early on, companies were largely paying cost per click (traffic) or cost per mile (impressions) on banner advertisements. As the technology evolved, the focus turned to commissions on actual sales or qualified leads. The early affiliate marketing programs were vulnerable to fraud because clicks could be generated by software, as could impressions.
Forms of new media have also diversified how companies, brands, and ad networks serve ads to visitors. For instance, YouTube allows video-makers to embed advertisements through Google's affiliate network. New developments have made it more difficult for unscrupulous affiliates to make money. Emerging black sheep are detected and made known to the affiliate marketing community with much greater speed and efficiency.