Using botnets to click PPC ads isn’t new.

But only recently someone has uncovered evidence that network of compromise PCs are being used to click on Adsense ads. The botnet clicking service is hired by publishers to click their Adsense ads while making sure the activity goes undetected by keeping it at a low level.

Pay-per-click schemes such as Google Adsense have programs to detect fraudulent clicks and suspend publishers implicated in click fraud. In an effort to disguise bogus visits, these publishers have begun hiring botnets to slip under the radar of fraud detection programs.
The “bottom line is that the advertiser pays in exchange for a bot visiting him”, the SANS Institute reports.

Generating traffic from a small number of machines (numbered in the hundreds) makes the traffic generated from compromised machines look innocuous. In return for helping click fraud scammers keep a low profile, botnet owners rake in a percentage from the scam.

Read more: Botnet implicated in click fraud scam