At its peak during its two-year existence, Kurupt.su -- a website specializing in the trade of stolen credit-card numbers -- had more than 6,000 members who bought and sold pilfered data in an online bazaar dedicated to defrauding consumers.
It was governed in part by "Fortezza," the nickname of an administrator who exercised tight control over who was allowed into the secret forum given its criminal nature. "Carding" websites are the bane of banks, victimizing consumers in a fast-moving global frauds.
U.S. prosecutors say they now have custody of Fortezza, aka David Benjamin Schrooten, a 21-year-old Dutch national who was extradited on Friday from Romania. Schrooten, who was indicted on 14 counts ranging from fraud, conspiracy, intentional damage to a computer and aggravated identity theft, has pleaded not guilty.
Fortezza stuck out amongst other users on Kurupt.su, said Dan Clements, a computer security expert who runs CloudeyeZ, a company that helps financial institutions and other organizations identity stolen data circulating online.
Clements had his eye on Kurupt.su as part of his business for some time. Fortezza, he said, wrote more than 1,000 posts on the forum in proper English -- a rarity given the mangled grammar usually found on such forums.
"He was quite fluent," Clements said on Wednesday in a telephone interview.
During his research, Clements was curious whether Fortezza might be a law enforcement officer, as FBI agents regularly try to gain access to such forums for investigations, posing as part of the criminal underground. After a few unsuccessful attempts, Fortezza responded to Clements via instant messenger.
And once Fortezza started chatting, "we couldn't shut him up," Clements said.
Fortezza managed Kurupt.su with an iron fist: people who wanted to join the website had to be vetted by another user. Vendors of stolen credit-card numbers who ripped off others were banned. Experts with CloudeyeZ were occasionally kicked off, but the company always had constant access due to several valid logins, Clements said.
According to Schrooten's indictment, prosecutors allege he and other co-conspirators hacked into other carding sites -- in effect, possibly stealing already stolen data. With Kurupt.su already doing a brisk trade in card numbers, hacking competitors' websites may have been more of an act of bravado than a criminal business necessity.
"In all of my instant messages with him, money was never his motivation," Clements said.
Curiously, while Schrooten's indictment accuses him of conspiring to "generate illicit financial proceeds" for his personal benefit, there is no estimate of how much he may have personally benefited.
But a criminal complaint filed against another 21-year-old American man, Christopher A. Schroebel, indicates how lucrative the data trade is. Schroebel, of Keedysville, Maryland, was accused of working with Schrooten, collecting stolen card numbers by installing malware on point-of-sale devices in two businesses in the Seattle area.
In March 2011, Schroebel allegedly transferred US$33,654.54 into his Bank of America account. Over the next three months, more than $85,000 was deposited, which prosecutors allege came from selling compromised account numbers and withdrawals made on stolen credit cards, the complaint says.
Schroebel, who is described in the complaint as at one time being an intravenous heroin user, has pleaded guilty to five counts and is awaiting sentencing, according to court records filed May 30 in U.S. District Court for the Western District of Washington.
At one point during their chats, Clements said Fortezza expressed an interest in trying to fight global cybercrime rather than be on the other side. Fortezza also expressed his concern that law enforcement might be onto him.
Clements has published his research into Kurupt.su. He noted that last December quarrels erupted between Kurupt.su and Kurupt.ru -- another carding site -- and that contact details for "David B. Schrooten" of Spijkenisse, the Netherlands, were posted on Kurupt.ru.
"He needs to learn not to [expletive deleted] with Russians," the post reads, according to an image on Clements' website.
The scenario is not unlike that of Max Butler, a talented hacker who built one of the largest-ever carding website, CardersMarket.com, and also hacked into other underground sites hosting stolen data. Butler's exploits are documented in the book, Kingpin. Butler was sentenced to 13 years in prison in February 2010.
Schrooten was arrested in Cluj, Romania, in March. He'd gone there to see his girlfriend, Clements said. After his arrest, Clements said he was in touch by e-mail with Schrooten's parents. Schrooten wanted his extradition to the U.S. sped up due to poor conditions in the detention facility where he was held, Clements said.
Clements said he went to Cluj to visit Schrooten but was not allowed because Schrooten had too many visitors by that point. During his detention in Romania, Schrooten attempted suicide twice, Clements said.
"I would say he's a complex young man," Clements said. "He had all those issues of power and ego."
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