The Federal Bureau of Investigation (FBI) said this week that hackers in Estonia have been arrested for using malware to replace legitimate Web advertising with their own ads, generating millions in revenue that would have instead gone to publishers.

Overall, some 4 million computers were affected by the scheme, which investigators called the "tip of the iceberg." Approximately 500,000 of those computers were in the United States, and even government agencies such as NASA were affected, they said.

The seven men, six from Estonia and one from Russia, allegedly used malware to redirect Internet searches and other legitimate Web traffic to pages containing real ads placed with fake companies the hackers set up, entitling them to hefty payments.

The scheme required the thieves to act as a middleman for advertisers and publishers, who often use collective networks to distribute new campaigns and bargain for better rates. Malware-infected computers would see fraudulent advertisements on real websites, like the home pages of The Wall Street Journal or ESPN, investigators said.

Money paid out by advertisers thinking they had received genuine click traffic was then laundered through a series of front companies, the FBI added.

Additionally, the malware disabled automatic updates on its host computers, leaving them vulnerable to other hackers going forward.

"The globalization of the legitimate economy was the inspiration for Thomas Friedman’s The World Is Flat. The global reach of these cyber thieves demonstrates that the criminal world is also flat," FBI Assistant Director in Charge Janice K. Fedarcyk said. "The Internet is pervasive because it is such a useful tool, but it is a tool that can be exploited by those with bad intentions and a little know-how. In this context, international law enforcement cooperation and strong public-private partnerships are absolute necessities, and the FBI is committed to both."

Photo illustration: Flickr user Sarah G..