Spanish authorities have collared three people believed to be behind the spread of a computer virus that infected around 13 million computers worldwide. Reports said the suspects are the leaders of the group behind the so-called Mariposa botnet, which steals credit card data and other bank credentials.

Investigators believe that the botnet has infiltrated around 500 of Europe’s top 1,000 companies and close to 50 major banks. Police officer Cesar Lorenza said the suspects are not the usual hackers, as all of them are not computer experts. The suspects, who were not named to preserve their rights as defendants, had received helped from hackers in building the botnet.

The Mariposa botnet first appeared in December 2008 and has since taken control of millions of computers to become one of the most dangerous cybercrime networks in the world. Authorities have yet to determine how much money the botnet has amassed before it was dismantled. The botnet was spread through peer-to-peer networks, removable thumb drives, and instant messaging, investigators said.