Chameleon botnet grabbed $6m A MONTH from online ad-slingers

Click fraudster bot fingered after analysts crack its signature

A web analytics firm has sniffed out a botnet that was raking in $6m a month from online advertisers.

The so-called Chameleon botnet mimicked human visitors on select websites, causing billions of display ad impressions to be served to compromised machines. As many as 120,000 infected drones have been discovered so far. Almost all of the over 202 websites targeted in the scam are located in the US. In some cases, two-thirds of the websites' traffic was generated from zombie machines.

All the bot browsers report themselves as being Internet Explorer 9.0 running on Windows 7.

The advertisers cough up a few pennies every time an ad is viewed, and the ad network, ad exchanges and the publisher all take their share.

The malign traffic was difficult to identify because the malware used a hundreds of thousands of different ad-exchange cookies. These characteristics earned the malware behind the scam the Chameleon moniker.

Click fraud as a revenue generation model for zombie networks is far from unprecedented. For example, the Bamital botnet taken down by Microsoft and Symantec last month also made money through advertising fraud. However the Chameleon malware is reckoned to be the most sophisticated botnet software of its type to appear to date.

Chameleon affects display ad advertisers and not just text link advertisers. Individual bots within the Chameleon botnet run on host machines with Microsoft Windows as the operating system. Bots access the web through a flash-enabled Trident-based browser that executes JavaScript.

The bots subject host machines to heavy load, and the bots appear to crash and restart regularly. These crashes and idiosyncratic site-traversal patterns are just two of the many bot features that provide for a distinctive bot signature that eventually allowed London-based web analytics firm spider.io to track fraudulent behaviour associated with the malware and draw up a blacklist of compromised IP addresses in association with its ad exchange partners.

"Spider.io has been tracking anomalous behaviour associated with Chameleon botnet since December, 2012, and in February of this year the extent of the Chameleon botnet’s principal web-browsing activity was established," an advisory by spider.io explains.

"This was achieved as part of spider.io’s broader work with leading display ad exchanges and demand-side platforms to identify deviant consumption of display advertising media. In particular, DataXu and Media6Degrees have been proactive partners."

Spider.io was born out of Imperial College London. ®

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