Spanish police have arrested three men thought to be responsible for one of the world's biggest botnets.
The men, all Spanish citizens, are accused of operating the Mariposa botnet, the BBC reported. Mariposa had infected an estimated 13 million computers in 190 countries, before it was taken down in December.
The botnet was designed to gather private information, including usernames, passwords and credit card data.
Parts of Mariposa were rented out to other cybercriminals, while stolen credit card information was used to make fraudulent transactions.
A number of high-profile targets had been infected, including half of the Fortune 1000 companies and around 40 major banks, investigators say. One suspect had 800,000 pieces of personal data stored on his machine.
The suspects reportedly had only rudimentary hacking skills, relying on pre-written malware distribution software to build the botnet.
Mariposa was shut down following a joint investigation by the Spanish police, the FBI and world security experts such as Defence Intelligence and the Mariposa Working Group.
Microsoft last week announced it had shut down another major botnet, Waledac, after receiving court approval to do so.