US authorities have charged seven people with spreading software to hijack millions of computers worldwide.
Six of them are Estonians, who have been arrested, while the seventh, a Russian, is still at large.
They are alleged to have spread software across four million computers in 100 countries that redirected users towards online adverts.
The defendants were allegedly paid about $US14 million by advertisers for the clicks the advertising pages received.
About 500,000 of the affected computers were in the US, the BBC reports.
Of those, 130 were at the space agency Nasa, which first discovered the malicious software.
US Attorney Preet Bharara said it was the first case of its kind because the suspects had set up their own servers to secretly reroute traffic to sites where they would get a cut of the advertising revenue.
People trying to visit sites such as Amazon, Netflix and ESPN were instead sent to the defendants' adverts, according to the authorities.