You get what you charge for. Facebook Flyers, the social-networking site's cut-rate advertising program, charges a $2 CPM — a rate that amounts to 0.2 cents per person who sees the ad. Those bottom-of-the-barrel prices draw bottom-of-the barrel sponsors: Dan Goodin at sarcastic British tech site The Register calls one ad "crudware ." The flyer ad encourages people to join a supposedly free dating network, but clicking on the ad instead launches a pop-up window claiming the user's computer has been infected and pitching antivirus software. Most sites have policies forbidding such ads, but Facebook, desperate for ways to make money off its 30 million users, seems to have no such qualms.