Authorities have smashed one of the world's biggest networks of virus-infected computers - a data vacuum that stole credit cards and banking credentials from as many as 12.7 million poisoned PCs.
The "botnet" of infected computers included PCs inside more than half of the Fortune 1,000 companies and more than 40 major banks, according to investigators.
Spanish investigators, working with private computer-security firms, have arrested the three alleged ringleaders of the so-called Mariposa botnet, which appeared in December 2008 and grew into one of the biggest weapons of cybercrime.
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More arrests are expected soon in other countries.
Spanish authorities have planned a news conference for Wednesday in Madrid.
The arrests are significant because the masterminds behind the biggest botnets aren't often taken down.
And the story of investigators' hunt for them offers a rare glimpse at the tactics used to trace the origin of computer crimes.
Underworld contacts
Also, the suspects go against the stereotype of genius programmers often associated with cyber crime.
The suspects weren't brilliant hackers but had underworld contacts who helped them build and operate the botnet, Cesar Lorenza, a captain with Spain's Guardia Civil, which is investigating the case, told The Associated Press.
Investigators were examining bank records and seized computers to determine how much money the criminals made.
"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," Lorenza said.
The three suspects were described as Spanish citizens with no criminal records.
They weren't named and their mug shots weren't released, which Lorenza said is standard in Spain to protect the privacy of defendants.
They face up to six years in prison if convicted of hacking charges.
Authorities identified them by their internet handles and their ages: netkairo, 31, jonyloleante, 30 and ostiator, 25.
Infected PCs 'hijacked'
Botnets are networks of infected PCs that have been hijacked from their owners, often without their knowledge, and put into the control of criminals.
Linked together, the machines supply an enormous amount of computing power to spammers, identity thieves, and internet attackers.
The Mariposa botnet, which has been dismantled, was easily one of the world's biggest. It spread to more than 190 countries, according to researchers.
It also appears to be far more sophisticated than the botnet that was used to hack into Google and other companies in the attack that led Google to threaten to pull out of China.
The researchers that helped take down Mariposa first started looking at it in the spring of 2009.
Chris Davis, CEO of Ottawa-based Defence Intelligence, said he noticed the infections when they appeared on networks of some of his firm's clients, including pharmaceutical companies and banks.
It wasn't until several months later that he realised the infections were part of something much bigger.
