Of the 350 million messages pitching pharmaceuticals, 10,522 users visited the advertised site, but only 28 people tried to make a purchase, a response rate of .0000081 percent. Still, that rate is high enough to potentially generate up to $3.5 million in annual revenue, they concluded. And that's why they do it. I would have laughed at the idea of a .0000081% response generating a profit, which is why I'm not a millionaire.