A teenage hacker from New Zealand who helped a criminal network to infiltrate more than 1 million computers worldwide and skim millions of dollars from bank accounts has been hired as a cybersecurity consultant by the country's second-largest telecommunications company.

Owen Thor Walker has skills that can help senior executives and customers understand the security threats to their networks, TelstraClear spokesman Chris Mirams told National Radio on Wednesday.

Walker pleaded guilty last year to a raft of charges connected to his work for an international network that the FBI estimated infiltrated some 1.3 million computers and skimmed bank accounts or damaged computer systems to the tune of more than $20 million.

He was 18 years old when he stood trial in July.

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The charges against Walker — who used the online name "AKILL" and wrote so-called botnet infiltration programs for the crime network — were dismissed and he was released without a criminal record after paying a fine and forfeiting cash paid by the criminal group for his expertise.

Walker has delivered a series of seminars for TelstraClear, advised senior security and management staff at the company and has taken part in an advertising campaign, Mirams said.

"It was really just ... to let them know the type of cyber threats that are out there, developing," Mirams said.

Walker told delegates what cyber criminals are trying to achieve and how to defend their networks against such threats, he said.

Some hackers send mass e-mails to a target corporate or government computer system to overload it and crash the system. Others assume control of thousands of computers and amass them in centrally controlled clusters known as botnets.

The hackers can then use the computers to steal credit card information, manipulate stock trades and crash industry computer systems.

TelstraClear is a wholly owned subsidiary of Australia's biggest telco, Telstra.