Hundreds of children – including 60 in the UK – at "significant risk" of abuse from named paedophiles have been removed from immediate danger after British police helped destroy what they believe is the largest online paedophile network in the world.

The three-year operation exposed more than 70,000 members across the UK, US, New Zealand, Australia and Thailand, and led to 184 arrests internationally, 121 of them in Britain.

The investigation, Operation Rescue, led by the UK's national centre for child protection, was joined by Europol, the US immigration and customs enforcement agency, and police from Australia, New Zealand, the Netherlands and Canada. It identified 670 suspects and 230 abused or at-risk children globally. Some of the first arrests were made in Thailand.

Police were unable to say how many children had been taken into care as a result of the investigation. One suspect, a scout master whose case is still pending, was arrested 24 hours before a camp where he was allegedly planning to abuse a named boy in his care.

Offenders were tracked to countries including Italy, Spain and Thailand. Details were revealed at a press conference in The Hague, the Netherlands, where the website's server was based.

The network hid behind boylover.net, a legal forum which attempted to function covertly by operating as a discussion-only forum where members could share their sexual interest in young boys without committing any offence. But members, having made contact, would then move to more private channels such as email to exchange and share images of children being abused.

In the UK, the 240 suspects included police officers, teachers and youth leaders, with an age range of 17 to 82. One of the UK suspects was a woman. To date, 33 have been convicted, including John McMurdo, 36, a scout leader from Plymouth, who was jailed in January last year after admitting possessing and distributing child pornography, and Lee Palmer, who was sentenced to six years in prison in March 2010 after pleading guilty to the sexual abuse of two boys, aged two and nine. Police discovered more than 60,000 indecent images on his computer.

Peter Davies, the UK police chief who leads the Child Exploitation and Online Protection Centre (Ceop), and is also the UK's lead for child protection, said: "The scale and success of Operation Rescue has broken new ground. Not only is it one of the largest operations of its kind to date – and the biggest operation we have led – it also demonstrates the impact of international law enforcement agencies working together with one single objective: to safeguard children and bring offenders to justice. That drive has been the hallmark of all the forces and teams involved.

"What we show today is that while these offenders felt anonymous in some way because they were using the internet to communicate, the technology was actually being used against them. Everything they did online, everyone they talked to or anything they shared could, and was, tracked by following the digital footprint."

Davies said all 230 children identified were at significant risk from named offenders but it was impossible to count how many had been rescued from future abuse "over the lifetime of these offenders". "There are occasions when the threat is so close that the only option is to take these children into care, but the risk can come from babysitters or neighbours. Most of them are individuals but there may be clusters."

He said one of the key messages from this operation is that the internet is not a haven. "My advice to young people is to think carefully when they go on the internet because they don't necessarily know who they are speaking to – and nor did some of these offenders, who found they were actually making contact with members of our international police team."

The founder and owner of the website, Amir Ish-Hurwitz, 37, from the Netherlands, was jailed by a Dutch court on Wednesday, triggering the decision to publicise the scale of the police operation. The site was closed down on the 25 November 2009.

"We could have publicised this earlier, or later, but once the website owner was in court it was obvious that information would emerge," said a Dutch police spokesman.

Operation Rescue began in 2007, after Ceop and Australian police independently found boylover.net. Three detectives then posed as members to identify those who posed the biggest risk to children.

The breakthrough came when officers were able to access and take over the account of the only UK administrator, based in Durham, and were able to see the personal details, including date of birth, occupation and country of residence of members. "We were amazed that they had registered their true occupations" said Kelvin Lay, a senior investigating officer and one of the three responsible for infiltrating the site.

Lay and the other officers identified those who had an occupation or hobby that put them in contact with children as grade A. He said: "We painstakingly went through every post and message to identify whether they were physically abusing children or had access to children." This process led to the 121 arrests.

The Europol director, Rob Wainwright, described the results of the investigation as "phenomenal" and praised analysts at Europol's headquarters for infiltrating the sophisticated computer codes designed to cover the tracks of those using the online forum to meet or exchange illegal images of children. He said: "The safeguarding of so many vulnerable children is particularly rewarding."

He added that Europol had so far issued more than 4,000 intelligence reports to police authorities in more than 30 countries, which had led to the arrest of suspects and the identification of abused children.

The website, boylover.net, had attracted a cross-section of professional workers including teachers, taxi drivers and IT consultants, he said.

As part of the operation, Ceop provided intelligence to Thai police in February 2008 about British nationals suspected of committing child sexual abuse in their jurisdiction. This led to Operation Naga in November 2008, during which four suspects were arrested, according to Ceop.