According to reports published, authorities in Spain have arrested three men in an operation of a massive botnet composed of 12.7 million PCs that stole credit card and bank log-in data and infected computers in half of the Fortune 1,000 companies and more than 40 banks.

The Mariposa botnet, which appears to be one of the worlds biggest, took over millions of computers, many of which continue to be hampered, security researchers posted Tuesday.

However, it's difficult to point the exact size of the botnet from that number, although its magnitude is really huge. Researchers studying the notorious Conficker botnet have associated it to half as many IP addresses.

The criminals are revealed to have used Mariposa for typical cyberscams, stealing banking credentials and initiated distributed denial-of-service (DDoS) attacks.

"They're not like these people from the Russian mafia or Eastern European mafia who like to have sports cars and good watches and good suits--the most frightening thing is they are normal people who are earning a lot of money with cybercrime", Cesar Lorenza, a captain with Spain's Guardia Civil, which is investigating the case, explained.