(Google) marketing techniques

HELSINKI - Computer specialist Didier Stevens put up a
simple text advertisement on the Internet offering downloads of a
computer virus for people who did not have one.
Surprisingly, 409 people clicked on the ad which read "Is your PC
virus-free? Get it infected here!" during a 6-month advertising
campaign on Google's Adword, said the IT security expert.
"Some of them must have clicked on it by mistake. Some must have been
curious or stupid," said Mikko Hypponen, head of research at data
security firm F-Secure.
There was no virus involved, it was an experiment aiming to show
how advertising systems can be used for malicious intent, Stevens
told Reuters.