The arrest of 100 people subscribing to the largest commercial child pornography ring ever discovered in the United States has called into question the assumption that Internet paedophilia is a non-profit-making activity. A two-year investigation, dubbed Operation Avalanche, came to a head yesterday when US attorney general John Ashcroft issued a string of arrest warrants for child pornography subscribers and merchants in the US, Indonesia and Russia. Among those charged were five international Webmasters, who remain at large. The child pornography network, operating under the name of Landslide Productions, took credit card payments over the Internet for access to pornographic images and films of children being sexually abused. Two children from Britain -- an eight-year-old girl and her six-year-old brother -- have been identified in the images that have been discovered so far. "The set-up was relatively unusual for a paedophile ring -- adult obscene material is often sold for profit, but paedophiles usually operate as a club," said Peter Sommer, a research fellow at the London School of Economics. Sommer acted as an expert defence witness at the Operation Cathedral trial in January, and explains that Wonderland was more typical, an elite group of people who used the Internet to swap images of children among themselves. New members would only be invited to join if they were identified as big "traders", and would take the trouble of hiding their identities from other paedophiles operating on the Web. Membership was dependent on bringing at least 10,000 indecent pictures of children to the club. Operation Avalanche was a nationwide investigation involving the Dallas police and the US Postal Inspection Service (USPIS), which first detected the Landslide ring. Postal inspectors were able to trace many of the Landslide customers through the credit card details used for Internet transactions. The Landslide Web site had an estimated 250,000 visitors, who paid $30 (£21) for a monthly subscription to the service. "I'm surprised that a paedophile Web site was able to last for so long," said Sommer. "Wonderland used a version of IRC, that can only be found if you know that it exists... but a Web site is very easy to locate." Thomas Reedy, who ran Landslide out of Texas, was arrested in 1999 and on Monday was sentenced to a total of 1,335 years in prison for the sexual abuse of minors, distribution of child pornography and conspiracy. His wife Janice, who managed the Web site's accounts, was sentenced to 14 years. "In technical terms, this wasn't a very difficult investigation," said Sommer. See the Net Crime News Section for the latest on hacking, fraud, viruses, child safety online and related issues. See the Internet News Section for full coverage. Have your say instantly, and see what others have said. Click on the TalkBack button and go to the Telecoms forum. Let the editors know what you think in the Mailroom. And read other letters.