The arrest of 50 people all over Europe and the seizure of scores of computers, hard drives and thousands of disks is the culmination of a complex and elaborate operation.

The National Hi-Tech Crime Unit and their colleagues in Europol had to use all their technical know-how to break into the Shadowz Brotherhood.

Paedophiles are naturally suspicious of newcomers into their social circle and, like many criminal groups operating in cyberspace, are skilled at counter-surveillance.



Child pornography constitutes a disgrace to human dignity.

Gilles Leclair

Europol

Neither Europol or the National Hi-Tech Crime Unit would comment on whether undercover police officers posed as paedophiles in order to infiltrate the ring.

But, reading between the lines, that is the only way the police could have accessed the Shadowz Brotherhood's website and gained the confidence of the other members.

A Europol spokesman said the group's activities centred around a website which had an archive of child abuse images.

He said that when uploading and downloading images to and from the site they used sophisticated encryption techniques, often hiding obscene material in apparently innocent picture files.

The website was run by a group of hardcore paedophiles called "administrators" who operated a star-rating system.

Girl identified

The administrators would vet new members, who would then receive a "one star" rating allowing them to enter fairly tame newsgroups and bulletin boards.

To gain further stars they had to upload images of child sex abuse for viewing and downloading by other members.

As they gained more stars they were allowed access to restricted sites and protected rooms containing the most perverted material.

An administrator would be on duty 24 hours a day to assess new images.

Proxy servers were used to disguise where members were accessing the site from and it is believed that special software was used to give those involved cyber anonymity.

BBC News Online's technology correspondent Mark Ward said criminal groups often used servers run by other innocent organisations to host illegal images.



Criminal groups take advantage of the high-tech technology to attack the principles and the values of our democratic systems

Gilles Leclair

Europol

He said many universities and other vulnerable organisations spent a lot of effort making sure their servers were not used by such groups.

He said paedophiles often met each other in prison and kept in contact afterwards, passing on codewords, information about sites online and advice about how to avoid scrutiny online

Most of those involved are believed to have taught themselves computer encryption techniques.

But Europol had its own team of intelligence analysts, working in a secure operations room in The Hague equipped with the latest technology.

They processed information received on a daily basis from investigators in the different participating states.

In March police monitoring the site identified a six-year-old girl and went to the US to take her away from a suspected paedophile.

Team of analysts

Detectives are expected to spend months trawling the suspects' hard drives in an attempt to locate images which would lead to convictions.

Europol said the Shadowz Brotherhood was formed in 2000, but some of its members had been in contact on the internet before that date.

Europol's deputy director Gilles Leclair, head of Serious Crime Department, said: "Child pornography constitutes a disgrace to human dignity.

"Criminal groups take advantage of the high-tech technology to attack the principles and the values of our democratic systems.

"But, once more, the international law enforcement co-operation proved very effective and gave a strong and decisive answer against organised crime."