After a man was nabbed in June for allegedly operating what appeared to be Japan's largest child pornography website, experts believe police are making progress in unmasking anonymous predators who engage in illegal and immoral activities on the dark web.

Facing a huge challenge because of the difficulty of identifying people who conceal their location by lurking in the recesses of the hidden internet, Kyoto Prefectural Police secured their breakthrough due to flaws in the exploitative website operator's own procedures.

Police were able to track down Mitsugu Ono, a 59-year-old man who operated the site named Lollitter2.onion, through data analysis and by contacting users who, like the investigators, had gone through the site's compulsory registration process.

To gain an understanding of the murky parts of the internet where sites hosting child porn, illegal markets and other services that are not always nefarious but have users which seek anonymity, Kyodo News reporters used Tor, one of the types of software that unlocks the encrypted space and allows communication and information transfer.

One Japanese child porn site's home page that reporters accessed showed young foreign girls, most appearing to be less than elementary school age, clad in underwear and bathing suits. There were forums, rankings, and even banner ads for Japanese anime.

Tor, which stands for The Onion Router, directs internet traffic through a network structured like the layers of an onion. It encrypts data, including IP addresses, multiple times and routes it on a random journey across multiple systems, making it nearly impossible to track and, therefore, identify the parties involved.

Although mainly thought of as a hotbed for criminal activity, the dark web is also used by whistleblowers in countries where free speech is not guaranteed and censorship makes sharing any anti-government views a potentially dangerous activity.

According to the Kyoto police, a 2015 study conducted by a British university found that around 45,000 hidden services could be accessed using Tor, including about 900 child porn sites.

"It is just the tip of the iceberg," said one high-ranking police official. "No one really knows what the real figures are."

The dark web -- which is also used by criminals to trade firearms, narcotics, counterfeit money and other contraband -- has become a refuge for pedophiles as authorities worldwide have ramped up efforts to eradicate child pornography from the open world wide web.

The same university study also concluded that more than 80 percent of dark web traffic accesses sites showing underage pornographic material.

(File photo shows computers, hard drives and DVDs confiscated by police in connection to child pornography investigations)

According to police investigators, the man arrested in the case operated more than 40 child porn websites, the most Japanese authorities have ever discovered. On them he had posted some 210,000 images of children.

Police initially struggled to make progress in the case due to the inherent difficulty of investigating on the dark web. But they were able to identify the man through data analysis and interviews with members of the site.

From the membership list, police were able to identify approximately 50 further Japanese users and are set to refer them to prosecutors on suspicion of violating the law prohibiting child prostitution and child pornography.

Last year, Japan reported a record-high number of child pornography cases, reflecting a police crackdown that was enabled by a massive list of child porn purchasers, including teachers and politicians, obtained in a separate investigation.

The Tokyo Metropolitan Police Department arrested four people in May 2017 over suspected sales of child porn DVDs on a membership website, leading to a series of further arrests.

Tetsutaro Uehara, a professor who specializes in cybersecurity at Kyoto's Ritsumeikan University, suggested the June arrest of Ono is only scratching the surface.

"(Police) haven't actually broken through the Tor system, but this was a major achievement in poking a crack in it. This offers an opportunity to actually reveal how the distribution of child porn happens, which can become a deterrent for future sex crimes," said Uehara.