WELLINGTON -- A New Zealand teenager was convicted Tuesday for his central role in a global cyber crime ring which infected at least 1.3 million computers worldwide and caused millions of dollars in losses.

Owen Thor Walker, 18, allegedly led a group of international computer hackers who infected computers worldwide and caused economic losses of $20 million.

The teenager pleaded guilty to six computer crimes in a court in Thames, near his home south of Auckland and is due to reappear on May 28 for consideration of pre-sentencing reports.

Judge Arthur Thomkins said although some of the charges carried maximum jail sentences of up to five years, he was not considering imprisoning Walker, who suffers from Asperger's syndrome, a mild form of autism.

Walker, whose online name was "Akill," began committing the alleged crimes while still at school, police said last year.

He designed a unique encrypted virus that was undetectable by anti-virus software, police said.

The malicious software allowed access to user names and passwords, as well as credit card details, and was used by other criminals to commit crimes.

New Zealand police cooperated with the Federal Bureau of Investigation in the United States as well as Dutch authorities to uncover the network.

The investigation started after an attack involving 50,000 computers crashed the server at the University of Pennsylvania in the United States in 2006.

Walker was living with his parents when he committed the crimes, but they believed he was doing legal computer programming work, a police statement said.