US prosecutors have charged seven foreigners in a massive internet fraud scheme in which over four million computers across 100 countries, including those of American government agencies and NASA, were infected with malicious software and USD 14 million were made through fake online advertising.

Six Estonian nationals Vladimir Tsastsin, Timur Gerassimenko, Dmitri Jegorov, Valeri Aleksejev, Konstantin Poltev and Anton Ivanov were arrested and taken into custody yesterday in Estonia.

The US Attorney's Office will seek their extradition to America. The seventh defendant, Andrey Taame, a Russian national, remains at large.

Each individual is charged with five counts of wire and computer intrusion crimes and faces up to 30 years in prison.

Terming the case the "tip of the Internet iceberg," US Attorney for the Southern District of New York Preet Bharara said of the four million computers infected worldwide in the fraud, at least 500,000 were in the US including computers belonging to agencies such as NASA, educational institutions, non-profit organisations and commercial businesses.

"These defendants gave new meaning to the term 'false advertising.' They were international cyber bandits who hijacked millions of computers at will and re-routed them to internet websites and advertisements of their own choosing?collecting millions in undeserved commissions for all the hijacked computer clicks and Internet ads they fraudulently engineered," Bharara said.

According to the indictment, between 2007 and October 2011, the defendants used malware to secretly alter settings on infected computers and digitally hijacked internet searches.