Adrian Ringland, from the British town of Ilkeston, Derbyshire, has admitted forcing schoolgirls to send him explicit pictures after he infected their computers with a Trojan horse.

36-year-old Ringland posed as a teenager called "Ant Jones" in a chatroom, in order to plant the malware onto girls' PCs. Victims believed they were opening a picture of their new online friend, but the attached file was really a Trojan horse that allowed Ringland to take over computers. Unemployed Ringland used information he stole from the childrens' PCs, and his ability to control their computers (using tricks such as opening their CD tray remotely), to blackmail them into sending more and more explicit pictures.

Royal Canadian Mounted Police traced Ringland to his home address in the United Kingdom, where he was arrested and bailed. This did not stop Ringland's activities who was later discovered having sex with a 14-year-old girl he had groomed over the internet.

"Pedophiles are able to use the internet in a variety of ways when hunting for children to abuse. That they are also using modern technology such as webcams to spy and take photos and movies of their victims will be a worry for any parent whose children have computers in their bedroom," said Graham Cluley, senior technology consultant for Sophos. "Childrens' PCs must be protected by the latest anti-virus software, security patches and firewalls. Young people also need to be given guidance as to how to behave safely online, to reduce the chances of falling being exploited by sick hackers."

In late August, Ringland pleaded guilty to two counts of indecency with a child, four counts of blackmail, 10 counts of making indecent photos and five counts of unauthorized modification of computers. Ringland's victims included a 14-year-old schoolgirl from Manitoba, Canada and three British girls - two aged 14 and one who was 13 years old. Charges of near identical offences in respect of two other Canadian girls aged 14 and 15 and a 15-year-old British girl were ordered to remain on file.

Ringland's sentencing has been scheduled for a later date.

"The Canadian and British authorities should be congratulated for bringing this case to a conclusion, especially as initially Ringland tried to blame his partner's teenage son," continued Cluley. "Sadly this isn't the first time we have heard of internet voyeurs taking over innocent peoples' webcams for their own perverted ends, and it's unlikely to be the last."

Sophos reported on a similar case last year of a Cypriot man who took compromising pictures of a teenager via her webcam, and threatened to send the pictures to her friends unless she posed naked. In February 2005, a Spanish student was fined for a similar offence.