Then, in October 2011, the hacking group Anonymous announced on 4chan that they were launching cyber-attacks on a large "dark net" child porn site called Lolita City.

Links on the dark web.

Like all of the sites Graham would soon become involved in, it was only accessible using Tor software which renders browsing invisible and unlocks sites, lists, galleries, shops, forums and the "Hidden Wiki" not available to mere "clear-net" (ordinary internet) users.

Anonymous – which had already hacked Sony, the Scientologists and the Recording Industry Association of America -- wanted to bring down the service and expose its users to police. In their view, Tor's ability to hide internet users should not be extended to child porn.

Anonymous called it Operation Darknet and Graham, browsing 4chan as Year 12 wound down, was intrigued. He had never heard of Tor or Lolita City (Anonymous did bring it down but only briefly; it's now permanently closed).

When he looked, however, he discovered the worst and most secretive creatures on the internet -- those who make and trade in child pornography. The great irony was that he was led there by the very people who were trying to expose it as evil.

An artist impression of Matthew Graham. Credit:Joe Benke

Then, though, Matthew Graham went a whole lot further.

As he moved from high school to La Trobe University, where he was a nanotechnology student, Graham was, from his bedroom at home, going on to become the king of this dark domain.

Matthew Graham has been linked to Peter Scully who faces murder, rape and human trafficking charges in the Philippines. Credit:Inquirer Mindanao

On Wednesday, Graham, now 22, admitted in the Melbourne Magistrates Court that he set up and administered an extensive empire of hidden "dark net" websites and online forums for paedophiles. Some featured real-life torture and horrific sexual acts with children, including babies and toddlers, a genre known as "hurtcore" and beyond the pale even for most paedophiles.

Prospective members needed to provide a defined amount of original video content in order to join his sites, with names such as "Hurt 2 The Core", and "Love 2 The Core".

Peter Scully, who was arrested and jailed in the Philippines. Credit:Joey P. Nacalaban

In his first explorations of the "dark net", Graham, going under the name "Lux", posted messages on some child pornography forums he found. He told a US journalist last year, as Lux, that he had latent paedophilic feelings as a teenager but when he discovered the trove of images on the dark net, those feelings took hold.

"At first I felt ashamed in myself for being attracted to such a thing but as time went on I slowly grew more accepting of myself. It wasn't until I came across the Tor pedo community that I was able to truly feel comfortable with attractions."

Police describe Graham as a "non-contact" paedophile, meaning that, although he allegedly facilitated abuse he did not physically do it himself. A detective familiar with the two-year investigation – by the FBI, Europol, Canadian and Australian police – said Graham was "meek" and was unlikely to win a "battle of wits or anything else".

"You will find some of them have an inhibition and they've convinced themselves it's wrong for them to abuse children but it's OK for other people to do it," the detective said.

"Maybe Graham just didn't feel he had the skills to groom someone but, if you'd left him long enough, he probably would have done."

The US journalist, Patrick Howell O'Neill, joined paedophile forums to investigate the dark web. He identified himself as a reporter and spoke to members through encrypted emails.

"Lux saw me talking to his peers and reached out to talk to me, especially because Lux was a notable member of the community," O'Neill said.

He described himself to O'Neill as a "strong believer in free speech" and said that, even though he didn't personally like hurtcore, he defended other people's right to enjoy it.

After his initial dabblings in the dark net, Graham found that the paedophile sites he joined had banned hurtcore.

So he set up a suite of sites and forums of his own, hosted at first by a service called Freedom Hosting, which was Tor's most popular hosting service for websites selling drugs and pornography. Freedom Hosting was shut down by the FBI in 2013.

The alleged owner, a 30-year-old Irishman called Eric Eoin Marques, was arrested and awaits trial.

Then Graham began hosting his own sites.

At the time he was still living in the family home, in a quiet street in South Morang. They sold the house abruptly last year after their son was charged. The new owners found graffiti scrawled inside a bedroom wardrobe declaring: "Parents should be afraid of raising children like us". They painted over it.

As a babysitter Graham had direct access to six children, three boys and three girls, all aged under 10.

One mother said she felt sick when he was arrested.

"We've all had to speak to our kids. He was always a bit weird but you didn't think anything like this."

A father said: "I knew him well, he was a good kid. We trusted him."

A student who knew Graham at Epping Secondary College said he was a normal student.

"There wasn't any sign [he was] troubled or had issues," she said.

Investigators have been able to link Graham to several other notorious online paedophiles, not least accused paedophile fellow Melbourne man Peter Scully, who is now facing murder, rape and human trafficking charges in the Philippines.

He has also been linked to Shannon McCoole, of Adelaide, otherwise known as Skee, a childcare worker who is now facing 35 years in jail for sexually abusing seven children and running a dark web child pornography site.

Graham also has links to 26-year-old New York man Christopher Grief, known online as Mookie, an alleged prolific user of one of Graham's hurtcore sites.

The continuing investigation into Peter Scully and a probe into the possible murder of a child in Russia rely on material allegedly hosted by Graham, police said.

Graham was initially investigated by Canadian police, the FBI and Europol before the case was handed to Victoria police's Taskforce Astraea and the Australian Federal Police.

He was charged in Melbourne late last year.

Graham last year turned informer on a Melbourne man who is now jailed (with his name suppressed) for abusing a young female relative and filming her. One of the videos includes the girl holding a sign addressing "Lux".