Microsoft takes down $2.7m click-fraud botnet

Microsoft has disrupted another massive botnet, involving some two million machines around the world - its largest takedown since it stepped up its battle against organised online criminals three years ago.

The company filed a lawsuit in Texas and won a judge's order directing internet service providers to block all traffic to 18 internet addresses that were used to direct fraudulent activity to the infected machines.

Law enforcement in many European countries served warrants at the same time, seizing servers expected to contain more evidence about the leaders of the ZeroAccess crime ring, which was devoted to "click fraud."

Because of the sophistication of the threat, Microsoft and its partners do not expect to fully eliminate the ZeroAccess botnet

The schemes cheat advertisers on search engines including Microsoft's Bing by making them pay for interactions that have no chance of leading to a sale. Microsoft said the botnet had been costing advertisers on Bing, Google and Yahoo an estimated $2.7 million monthly.

The coordinated effort marks the eighth time Microsoft has moved against a botnet and a rare instance of it doing serious damage to one that is controlled with a peer-to-peer mechanism, where infected machines give each other instructions instead of relying on a central server that defenders can hunt down and disable.

Microsoft Assistant General Counsel Richard Boscovich said it "was built to be resilient to disruption efforts, relying on a peer-to-peer infrastructure that allows cybercriminals to remotely control the botnet from tens of thousands of different computers".

But the ZeroAccess botnet still had a weakness: the code in the infected machines told them to reach out to one of the 18 numeric IP addresses for details on which ads to click.

Microsoft recently opened its new Cybercrime Center in Redmond and is using new tools in its efforts. They are helped by a provision in trademark that allows pretrial seizure of suspected counterfeit goods, including websites that, as in the present case, are spreading tainted versions of the Internet Explorer browser.

The company is working with national computer security authorities in various countries and with Internet service providers to notify individual computer owners with infected machines, hoping to reach most of them before the fraudsters can spread new instructions.

Microsoft has been sharing evidence with the FBI and Europol, the continent's law enforcement coordinating service. National agencies took part in seizure actions in Germany, Switzerland, Latvia, Luxembourg, and the Netherlands.

For now, at least, the fraud by this network has stopped, said Boscovich. "Because of the sophistication of the threat, Microsoft and its partners do not expect to fully eliminate the ZeroAccess botnet," he admitted. "However, we do expect this legal and technical action will significantly disrupt the botnet’s operation".

The operators of the botnet are believed to be in Russia, while the author of the malicious software distributed on it could be based elsewhere, Boscovich said.