(AP) -- An FBI official said Friday a two-year-long multinational investigation led them to nab a 23-year-old Slovenian, who allegedly created a malicious software code that infected 12 million computers worldwide.
Stephen Gaudin, a legal attache of the FBI to the U.S. embassy in Vienna, Austria, told reporters that the cooperation between the FBI, Slovenian and Spanish forces was "unparalleled."
Slovenian police detained and questioned the man, identified only by his code name Iserdo, ten days ago, in the northwestern industrial city of Maribor. He was released after questioning, but police say they have made sure he cannot tamper with evidence or flee the country. They have not given details of how they have ensured that.
The investigation is ongoing and Iserdo was not formally indicted yet.
He is suspected of selling the malware to the operators of the Spanish Mariposa botnet - a network of infected computers - which stole credit cards and online banking credentials.
The Mariposa botnet, which has been dismantled, was easily one of the world's biggest, infecting hundreds of companies and at least 40 major banks in 190 countries since appearing in Dec. 2008.
Toni Kastelic, the head of Slovenian police cyber crime department, said police also questioned another, 24-year-old person, and confiscated 75 computers in seven house searches.
Kastelic said they were tipped off by FBI in April.
He didn't identify the chief suspect, Iserdo - which, read backwards, means "salvation" in Slovenian.
Kastelic said Iserdo sold his code to "a bigger number" of customers, who paid between euro100 ($130) and several thousand euros (dollars) for it, depending on the version. His chief buyers were from Spain, he said.
Iserdo was detained five months after Spanish police broke up the massive cyberscam, arresting three of the alleged ringleaders who operated the Mariposa botnet. They are being prosecuted for computer crimes.
The FBI said earlier this week that this case was significant because it targeted both the creator and operators of the malware. It also said more arrests are expected.
Slovenian media haven't disclose the identity of Iserdo either, only saying that he was a former student of the Maribor Faculty of Computing and IT.
Explore further: Facebook abuses 'quasi-monopoly' on user data, EU lawmaker says