A New Zealand teenager is facing a 10-year jail term after being accused of leading an international group of computer hackers called the A-Team that infiltrated more than a million computers worldwide and swindled their owners out of £12.5m .

The 18-year-old, working from his bedroom, is said to have collaborated with American associates in hijacking hundreds of thousands of computers around the world.

The case is part of an international crackdown on hackers who create networks of computers known as "botnets" to access personal bank accounts, steal credit card information or bombard users with spam. Eight people have already been charged, pleaded guilty or have been convicted since the operation under the auspices of the FBI began in June and more warrants are pending in the US and overseas.

The 18-year-old known only by his online identification AKILL, cannot be named because he was underage when the offences are alleged to have happened. He has cooperated with police in the North Island city of Hamilton, telling them how the crime system works, and was last night released on bail.

"He is very bright and hires out his skills to others," said Martin Kleintjes, head of the police electronic crime centre.

He said possible charges against the teenager could involve having unauthorised access to computers and possessing computer hacking tools. Police allege the youth wrote software that evaded normal computer spyware systems and then sold his skills to hackers around the world.

Hackers routinely send out viruses, worms and malicious Trojan horse programs which allow them to take control of a victim's machine. Using the internet to connect these "zombie" PCs, criminals are able to coordinate massive hi-tech strikes on particular targets.

Linking together thousands - or even millions - of machines into a robotic network attackers can send out billions of spam emails or swamp their victim with unwanted internet traffic. Hackers often try to blackmail large web businesses, banks and other groups reliant on being connected to the internet, by threatening to overwhelm them with millions of simultaneous attacks.

The New Zealand teenager is also suspected of being involved in crashing the University of Pennsylvania engineering school server in February 2006, along with 21-year-old Ryan Goldstein, who was charged earlier this month in the US. Officials said that the server, which usually handled about 450 daily requests for internet downloads, instead got 70,000 requests over four days. The FBI followed the trail and arrested Goldstein, who has pleaded not guilty, and then traced the New Zealand teenager.

The arrest comes as part of the FBI's Operation Bot Roast II - the second phase of its campaign to tackle hackers who set up and run botnets for criminal gain.

"Today, botnets are the weapon of choice for cyber criminals," said FBI director Robert Mueller in a recent statement. "They seek to conceal their criminal activities by using third-party computers as vehicles for their crimes."

Because they use zombie PCs to do their dirty work, the criminals are often virtually untraceable, said one expert.

"A lot of these guys consider it to be a victimless crime, but the thing they rely on is that the chances of being caught are very low," said Paul Vlissidis , of IT security company NCC Group.

Earlier this week computer security company McAfee warned that cyber terrorism was on the rise, with computer espionage and internet attacks posing the greatest threat to the net's future.

In the past year there have been reports of strikes against government targets in the US, Britain, Germany and India. The actions have been mainly attributed to hackers based in China, but Beijing has rejected claims of involvement.

Hackers

Raphael Gray: The unemployed Welsh 19-year-old famously hacked Microsoft founder Bill Gates's credit card details and sent him a shipment of Viagra in 2001. He was sentenced to three years' community rehabilitation.

Kevin Mitnick: The FBI launched a three-year manhunt to stop him from breaking into networks and stealing software at companies including Motorola. He was jailed but now advises companies on cyber crime.

The Pentagon hackers: Two California teenagers were given three years' probation in 1998 for assaults on sensitive military computers.

Joseph McElroy: In 2004 a teenager escaped jail after sparking a nuclear panic by hacking into a top secret US research centre. He triggered a slow-down that caused technicians to press "the panic button".