Online advertising is a multi-billion dollar business mostly ran by Google, Yahoo or Bing via AdSense-like programs. The current generation of clickbots such as the Redirector.Paco Trojan have taken abuse to a whole new level, burning through companies’ advertising budget at an unprecedented pace.
The malware’s objective is to redirect all traffic performed when using a popular search engine (such as Google, Yahoo or Bing) and replace the results with others obtained from a Google custom search. The goal is to help cyber-criminals earn money from the AdSense program.
Google’s AdSense for Search program places contextually relevant ads on Custom Search Engine’s search results pages and shares a portion of its advertising revenue with AdSense partners.
To redirect the traffic the malware performs a few simple registry tweaks. It modifies the “AutoConfigURL” and “AutoConfigProxy” values from the “Internet Settings” registry key so that for every request that a user makes, a PAC (Proxy auto-config) file will be queried. This file tells the browser to redirect the traffic to a different address.