Ian Frost, left, and Paul Rowland.
Operation Alpine, a four-year investigation, which ran from a secret county location and spanned the globe, led to a couple from Martin Dales, near Woodhall Spa, and their colluders being brought to justice.
Ian Frost, 35, pleaded guilty to distributing indecent images of children at Nottingham Crown Court yesterday, while his partner Paul Dean Rowland, 34, pleaded guilty to distributing, making and possessing indecent images of children.
Frost's brother, Paul David Frost, 37, of Woodhouse, Sheffield, pleaded guilty to distributing indecent images of children.
A fourth man, Ian Richard Sambridge, 32, from St Albans, Hertfordshire, also pleaded guilty to distributing indecent images of children.
Ian Frost and Rowland were the kingpins of an outfit which ran a UK-based "news service" website offering more than 1,300 suspected paedophiles in 45 countries access to millions of child abuse images. They, along with Sambridge and Paul Frost, profited to the tune of £2.2 million between 2002 and 2009.
They distributed indecent images of children to customers, including teachers, police officers and youth workers, who paid for them through websites set up by the group including AthenaNews.com
The service operated via a server in West Yorkshire which was further linked to a server in Manhattan, New York City. It had customers all over the globe in European, Asian, American and African countries.
The investigation revealed 211 UK
suspects and resulted in 178 premises being searched and 38 people being convicted.
The case was brought by Lincolnshire Police who worked with the Child Exploitation and Online Protection centre, along with other police forces.
The case was unprecedented for Lincolnshire Police.
Assistant Chief Constable Roger Bannister said: "The protection of children has always been the key objective of this investigation and the guilty pleas from four defendants is really pleasing in terms of us achieving what we set out to achieve.
"For me, this investigation was groundbreaking.
"As a senior investigating officer, I have a led a number of investigations of that type and magnitude but Operation Alpine was very different.
"The investigation has been challenging in many ways, particularly around the complexity of the technical side but also the international side and the 45 countries with which we have been involved.
"This was truly a team effort and there are a great many people to thank. The investigation team has worked tirelessly and very hard, for example, examining five-and-a- half million images."
The four will be sentenced in June with a date to be confirmed.