A hacker who used a Trojan horse to take control of computers belonging to adolescent girls in the UK and Canada has been sentenced to 10 years in prison.

Adrian Ringland, 36, of Ilkeston, Derbyshire, admitted to sending Trojan horse applications through Microsoft's instant messaging program to the girls, which then allowed him to control their computers, according to a Crown Prosecution Service (CPS) spokeswoman. The girls, who Ringland met through chat rooms, were between 13 and 16 years old.

He demonstrated his control of the girls' computers by remotely opening and closing the disc drive or turning off the monitor, while pressuring his victims to send naked photos of themselves.

Having obtained the photos, he then threatened to disclose them to the girls' friends and family using contact information he had stolen from the machines, unless they sent further photos.

One of Ringland victims sent a photo of herself topless, which Ringland then posted as wallpaper on her computer's desktop.

"It was to prove the power he had to help him with blackmail," the CPS official said.

Ringland pleaded guilty to two counts of unauthorised modification of a computer under the Computer Misuse Act, three counts of blackmail, six counts of making indecent photos of children and one count of indecency with a child.

Ringland was eventually reported to the Royal Canadian Mounted Police, which started an investigation that included the US Federal Bureau of Investigation, Microsoft and Britain's Serious Organised Crime Agency, the CPS official said.