The site's downfall was triggered by lucky law enforcement breaks, court fillings show (Representational)

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

Federal prosecutors with the U.S. attorney's office in the District of Columbia 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-style 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 killing 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 Liu of D.C.

"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, which 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.

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 those 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.