Even by the increasingly sophisticated standards of Internet child pornographers, the Wonderland club revealed by police in 12 countries yesterday operated on a technological and organisational level which shocked investigating authorities around the world.
Membership was on a strict invitation-only basis, and nominations for new members had to be approved by senior figures.
The club restricted its membership to people already among the most active in the netherworld of cyberspace's child sex scene.
One of the basic criteria before a candidate could even be nominated for membership was that they had to be in possession of at least 10,000 images of child pornography. And not just any 10,000 images; each had to be different from any of those held by other members.
It is this aspect which most alarmed child-protection agencies and police, and which sets the Wonderland club apart from other paedophile rings.
"Just to get through the door members had to already have access to an incredible number of images," said Mr Ruben Rodriguez, of the US-based National Centre for Missing and Exploited Children. "I think we can conclude from that that we are talking about the hard core of Internet child pornographers."
Wonderland's closed network on the Internet was protected by an extremely advanced security system. Unconfirmed reports from the US claim it used a code originally developed by the KGB to encrypt all its communications.
In the end, it was not high-tech scanning and tracking of Internet sites which revealed the club's existence. Instead the mammoth global investigation, code-named Cathedral, which led to yesterday's arrests was initiated by an investigation by US police into a routine allegation of child abuse.
In June 1996 the mother of a 10-year-old girl in a southern Californian farming community contacted police after her daughter complained that she had been abused by the father of a friend when she had stayed at their house overnight for a slumber party.
Local detectives discovered that the man's house contained digital equipment capable of broadcasting live pictures of abuse on the Internet, and computer files containing pornography.
Shortly afterwards another man was arrested, and the FBI and US Customs were called in.
It emerged the two men were part of an international paedophile ring, known as the Orchid Club, which was abusing children as young as five and broadcasting pictures across the net.
According to the California state indictment, the club's activities included the videotaping of a five-year-old girl somewhere in the mid-western US states, while at least 11 men had watched and asked to see particular forms of abuse.
The investigation identified three Britons involved in the club, one of whom lived in Hastings. Tipped off by US Customs, Sussex police officers raided the man's house and seized his computer equipment. This revealed the existence of the far bigger and more sophisticated ring which styled itself the Wonderland club.
Sussex police handed the investigation over to the National Crime Squad, which in turn passed information to police forces in the other 11 countries.
As well as being faced with the encryption system, police found the Hastings computer identified not real people but merely the nicknames they used to communicate.
Investigators in each country then had to link the screen name to an Internet service provider which was contacted to establish the identity of the user. The bulk of the membership appears to have been in the US.
Yesterday's swoop does not mark the end of the operation. Officers must attempt to identify the children involved, some of whom could now be middle-aged.