An article in BusinessWeek about the adware cash cow:
…Edelman shows how ads purchased for placement on Yahoo and partner sites by companies such as Cablevision Systems Corp. (CVC ) were also redistributed until they showed up as pop-ups. According to Edelman, Yahoo became blind to the trail of its own ads. One partner, Ditto.com, presented a Yahoo ad through another site, NBCSearch (not affiliated with the TV network). That company passed it along to one of its own partners. (NBCsearch and Ditto.com did not respond to requests for comment.) Sometimes, the ads showed up in pop-ups from spyware programs. In a prepared statement, Yahoo says it "takes the quality of its search ad distribution network very seriously. We are carefully investigating the claims that have been raised."