That ad fraud is carried out through personal computers is one of its most striking characteristics. The hacked personal machines, called drones, combine to form botnets, or droves of computers browsing the internet in a coordinated dance meant to grab as many advertiser dollars as possible. Taking over personal machines helps botnet operators avoid detection. It diversifies their IP addresses and geographic locations, masking the loads of traffic they send across the internet. Exploits can make their way onto computers via a number of paths, including through Wi-Fi networks, ads containing the code (malvertising), hijacked home routers, spam emails and hacked websites. (The Google team sneaked an exploit into the copy of Ad Age's site on the computer I was sitting at through a corrupted connection.) When you run into one of these scenarios, the exploit can unlock your machine without any sign something bad is occurring. "Normal users won't really see that something is going on," Sasha explained. You don't even have to click to get infected. Get the full story at Advertising Age Read also "Why Google's click-to-buy ads would be a big deal"