Security Experts:

Massive Botnet Stealing Millions of Dollars Per Month From Advertisers

A botnet called Chameleon, researchers say, is responsible for stealing $6 million per month from advertisers online, by emulating human traffic. The research and warning comes from, who published details on the botnet and a list of some of the largest hosts.

“Chameleon is a sophisticated botnet. Individual bots run Flash and execute JavaScript. Bots generate click traces indicative of normal users. Bots also generate client-side events indicative of normal user engagement. They click on ad impressions with an average click-through rate of 0.02%; and they surprisingly generate mouse traces across 11% of ad impressions,” a researcher report on the botnet explains.

Botnet ImageThe botnet seems to focus itself on 202 websites, these websites combined generate 14 billion ad impressions per month, and Chameleon represents at least 9 billion of them. Advertisers are currently paying $0.69 CPM to display ads to the 120,000 systems that are believed to be the core of the botnet itself. The researchers were able to determine that of the 202 websites that are the focus of Chameleon, the botnet accounts for 65% of their traffic. Based on IP, the bots all reside in the U.S., primarily in the residential sector.

“Despite the sophistication of each individual bot at the micro level, the traffic generated by the botnet in aggregate is highly homogenous. All the bot browsers report themselves as being Internet Explorer 9.0 running on Windows 7. The bots visit the same set of websites, with little variation. The bots generate uniformly random click co-ordinates across ad impressions and the bots also generate randomised mouse traces,” the research note continues.

Missing from the report is the list of 202 websites targeted by the botnet, which would help determine the advertising networks that are being scammed, and either confirm or exclude a link between the botnet operators and the sites themselves.

However, it’s still solid research from the crew at, which is known for tackling problems with automated traffic. It’s also interesting to note that Chameleon is – at least when it comes to the size of financial impact – 70 times larger than the Bamital botnet that was taken down by Microsoft and Symantec last month.

Bamital hijacked search engine results, often directing victims to websites the attacker controlled. From there, Bamital had the ability to serve additional malware and exploits from the attacker’s domain, but it could also be used to generate advertising impressions and ad clicks. When compared to Chameleon though, it’s a small packet fish in an ocean of traffic.

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Steve Ragan is a security reporter and contributor for SecurityWeek. Prior to joining the journalism world in 2005, he spent 15 years as a freelance IT contractor focused on endpoint security and security training.