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Friends say Owen Walker is a "brilliant" loner who got involved in a computer scam for a bit of fun.
But an international team of cyber-crime investigators accuses him of masterminding a fraud involving more than one million computers and $26 million.
The 18-year-old from Whitianga was the New Zealander spoken to this week as part of investigations by the FBI, the US Secret Service, Dutch authorities and police in New Zealand.
It is alleged he had control over a vast network of computers known as a "botnet", which cyber-criminals paid to use.
Friends said Walker was a brilliant computer programmer. He worked for Trio Software Development, a computer firm at Coroglen, near Whitianga.
He attended Mercury Bay Area School, but was home schooled from Year 9. Described by some as a loner, he is also a keen poker player.
Waikato police crime services manager Detective Inspector Peter Devoy would not confirm Walker's identity last night, but said officers had interviewed an 18-year-old who used the cyber ID Akill.
He had not been charged, but would be interviewed further once tests were done on seized equipment and police had a better understanding of the nature and extent of his activities.
A friend said Walker was "pretty shaken up" and police had taken all his electronic gear.
His mother yesterday refused to let the Weekend Herald talk to him, and declined to make any comment.
Walker told another close friend that he "did it for fun" at first.
The FBI told the Weekend Herald that the Whitianga teenager was part of "an elite international botnet coding group" responsible for infecting more than one million computers and contributing to losses of US$20 million ($26 million).
Walker - also known as Snow Whyte - was found during an 18-month investigation.
The FBI said his activity went beyond malicious. It said Akill was the co-conspirator in an attack in February last year that brought the computer network of the University of Pennsylvania to a halt, denying access to 4000 students and staff.
Akill and a 21-year-old American allegedly infected 50,000 computers with "malware" to infiltrate the university network.
"Malware" refers to programs such as viruses, adware and spyware installed remotely through the internet without the computer owners' knowledge.
From New Zealand, Akill is said to have created a unique virus that was undetectable by anti-virus software.
As well as allegedly heading the group - known as the "A-Team" - Walker was also allegedly involved in an illegal adware scheme that infected 1.3 million computers and was detected by Dutch investigators.
New Zealand e-crime national manager Maarten Kleintjes would not identify the teenager spoken to by police, but said his young age had surprised officers.
"He's very, very bright in terms of his ability to produce this sort of code," he said. "It's the first time we have got somebody of that magnitude in New Zealand, that's for sure."
As the net closed around Walker, the FBI sent an agent from the United States to help Waikato detectives.
Raids were made on Walker's home, and two properties in Northland and Canterbury on Wednesday.
Police now believe their targets in Northland and Canterbury were victims rather than conspirators.
