Underholdning writes: "As part of an experiment security researcher Didier Stevens bought a Google ad six months ago that said, "Is your PC virus-free? Get it infected here!" 409 people clicked on the ad. Didier writes that during those six months, the ad was displayed 259,723 times and clicked on 409 times. 98% of the machines ran Windows. Now that's a pretty cheap way of acquiring zombies."