U.S. and international law enforcement authorities have shut down one of the world’s largest child pornography websites following a raid and the arrest of Jong Woo Son, the underground site’s alleged South Korean-based administrator, federal officials said Wednesday.

Federal prosecutors with the U.S. attorney’s office in the District as well as IRS and Homeland Security Investigation officials called the “Welcome to Video” website one of a host of bitcoin-based, online bazaars that filled the vacuum after the 2013 takedown of Silk Road, a notorious “eBay” black market exchange for narcotics, prostitution and other dark net contraband.

Since Silk Road’s demise, U.S. authorities have charged rivals such as Wall Street Market and Valhalla as they emerged to take its place, but each has usually explicitly barred users from trading child pornography or soliciting murder-for-hire.

Welcome to Video’s site, however, only warned users not to upload adult pornography, U.S. prosecutors have said in court filings.

At the time the site was seized in March 2018, investigators found that thousands of the more than 250,000 unique video files were linked to search terms for “preteen hardcore,” “pedophile” and references to sex involving children as young as 2 and 4 years old, according to court filings.

Since then, U.S., Korean and British authorities have been unmasking the website’s previously anonymous users, tracking server data to prosecute customers for making illegal payments, illegal downloads or uploading videos, and for widening the child pornography distribution network.

“The sexual exploitation of children is one of the worst forms of evil imaginable. Indeed these crimes are so heinous they are difficult even to speak about, but our government has no higher priority than the safety or our children,” said U.S. Attorney Jessie K. Liu of the District.

“Let today’s announcement send a message: If you are involved in crimes of this nature, we are coming for you,” said Deputy Assistant U.S. Attorney General Richard Downing. They were joined by Superintendent General Oi Chul Yun of the Korean National Police and other U.S., British and Korean authorities.

Son, 23, who allegedly operated the site, has been indicted in U.S. District Court in the District of Columbia on nine counts of conspiracy, producing, advertising and distributing child pornography and money laundering. The government has also moved to seize 24 bitcoin accounts in a civil forfeiture proceeding.

Son has also been charged and convicted in South Korea, where he is serving an 18-month sentence, Liu said. Liu declined to comment on whether U.S. authorities sought his extradition.

Another 337 alleged users have been arrested around the world, based on leads shared with 38 countries, and 92 individuals have been investigated in the United States, with many prosecuted, U.S. officials said. About 23 children have been rescued from active abuse in the United States, Spain and the United Kingdom, officials said.

The site’s downfall was triggered by lucky law enforcement breaks, high-technology sleuthing and Son’s mistakes, court filings show.

Like its precursors, Welcome to Video operated as a hidden site accessed via the Tor web browser that hides the location of the websites and their viewers. Users created a free account and could download videos using credits earned by posting videos depicting sexual exploitation of children; referring new users; or using points purchased through bitcoin, which allows for nearly anonymous payments, prosecutors allege.

Around Sept. 1, 2017, however, law enforcement agents clicking on the website’s homepage found its source code “had failed to conceal an IP address, likely due to user error on the part of the administrator,” according to court filings.

Prosecutors contend the address was registered to Son and was serviced at his home in South Korea. Investigators set up undercover accounts to use the site, traced four email accounts allegedly used by Son and traced his Internet usage including searches for the website, bitcoin and child pornography.

A U.S. magistrate signed a sealed warrant for Son’s arrest in February 2018, and South Korean authorities searched his home a month later and seized Welcome to Video’s server and storage media, which they copied and gave to the FBI, prosecutors said.

The computer files contained child pornography, according to court filings. They also included customer data linking users to payments, and the payments to video downloads and “co-conspirators” who uploaded content to the site, authorities said.

Son was indicted that August under seal. Prosecutors alleged that between June 2015 and March 2018, Welcome to Video received more than $370,000 in at least 7,300 bitcoin transactions, including from users in the United States, United Kingdom and South Korea. Videos from the site were downloaded more than 1 million times, with some graphically showing sexual acts on children as young as 6 months old.

Wednesday’s announcement came days after Attorney General William P. Barr escalated demands on the technology industry to give law enforcement access to encrypted communications, calling it unacceptable for providers such as Facebook to deliberately design systems “to preclude any form of access to content” even to fight terrorism, organized crime and child exploitation.

Justice Department officials say takedowns of the Welcome to Video, Silk Road and other sites already test the limits of the FBI’s technological capabilities, and warn that “going dark” by encrypting communications and shielding data storage will put vastly more digital information beyond the reach of federal investigators even armed with a court order.

Cybersecurity experts counter that encryption is a critical tool to protect consumers’ data from hackers, and that the government can find other ways to gather evidence about criminals. Technology executives argue that access keys sought by law enforcement would create structural weaknesses that could be exploited by hackers, making everyone’s information less secure.

Downing, head of the Justice Department’s criminal division, said operators of anonymization services such as Tor “must ask themselves whether they are doing their part to protect children.” He added, “Society must decide whether it will accept these lawless online spaces.”

The volume of images of child sexual abuse has grown exponentially online, from fewer than 1 million reported more than a decade ago to 45 million last year, inundating technology platforms with images of victims subjected to sexual abuse, assault and even torture.

A study published last month by researchers and the National Center for Missing and Exploited Children said that reporting clearinghouses and law enforcement authorities are at “a breaking point,” unable to keep up with criminal activity and advances with smartphone cameras, social media and cloud storage. “NCMEC’s manual review capabilities and law enforcement investigations no longer scale,” calling for the use of machine learning and artificial intelligence tools to tackle the global spread of the problem.

Some outlines of the investigation were visible in previous prosecutions, in which the government had withheld the website’s name, it said, to avoid tipping off users.

Three cases have been brought by U.S. prosecutors in the District, including that of Nicholas Stengel, 45, of the District, who was sentenced in October 2018 to 15 years in prison after pleading guilty to money laundering and receiving child pornography. In his plea, he admitted paying about $377 in bitcoin and downloading 2,686 videos from the Welcome to Video site totaling more than 455,000 hours over a six-month period in 2017.

When FBI agents searched his home, Stengel, a former executive chef and wine store owner, attempted to kill himself, according to plea and sentencing papers, and, pointing to a computer, told agents, “That is what you are looking for.”

Also charged is Vincent Galarza, 29, of Queens, N.Y., accused in December of knowingly conspiring to distribute child pornography through interstate commerce. Galarza entered plea talks, his defense said in court filings, after authorities said they linked accounts in his name to 560 videos depicting child pornography uploaded to the website from June 25 to Dec. 21, 2016, and to 174 video downloads.

A third man, Brian Laprath of San Diego, was sentenced to 18 months in prison after pleading guilty to money laundering for using bitcoin to download at least five videos from the site, including two whose titles said they involved 12- and 13-year-old children.

An attorney for Stengel declined to comment, as did Galarza and Laprath’s attorney.