Law enforcement has taken down the world's largest child pornography site on the dark web and arrested its operator and 337 of its users across 38 countries.

The US Justice Department on Wednesday unsealed an indictment against South Korean national Jong Woo Son for running "Welcome to Video," a site that's been selling child porn to users across the globe since at least 2015.

Authorities actually arrested Son in South Korea and pulled the plug on Welcome to Video last year. They also seized the server he used to operate the site, which contained 8TB or more than 250,000 unique videos containing child pornography. "Forty-five percent of the videos currently analyzed contain new images that have not been previously known to exist," the Justice Department said today.

Welcome to Video was selling the videos in exchange for Bitcoin, making it among the first dark web websites to monetize child exploitation videos using the cryptocurrency, federal investigators say.

"In fact, the site itself boasted over one million downloads of child exploitation videos by users," the DOJ added. "An analysis of the server revealed that the website had more than one million Bitcoin addresses, signifying that the website had capacity for at least one million users."

(Welcome to Video screenshot. Source: Justice Department)

Welcome to Video was hosted on the Tor network, which is designed to help users and website creators operate with anonymity. However, investigators were able to the seize the server to the child pornography site, which enabled them to identify and nab its users. In the US, federal agents ended up searching the residences and businesses of almost 100 individuals. During the investigation, 23 victims who were being abused by users of the site were also rescued.

Investigators started to piece together the site operator's identity in 2017 when the homepage source code revealed two IP addresses from which the site was operating. They were traced back to a telecommunications provider in South Korea, and both IP addresses were also registered to 23-year-old Jong Woo Son.

Son has already been convicted in South Korea and is currently serving his sentence in the country. In today's announcement, federal investigators also called out Bitcoin for enabling the child pornography site to thrive. By using the cryptocurrency, buyers on the site could effectively make anonymous transactions. Over a three-year period, Welcome to Video took in at least 420 bitcoins worth over $370,000 at the time of the transactions.

However, the same Bitcoin transactions also helped investigators identify users on the site. This involved sourcing the Bitcoin payments from Welcome to Video back to the third-party cryptocurrency exchanges, which then revealed information on the account holders.

Although Son is already serving his sentence in South Korea, the Justice Department today also publicly named charges against 36 users of the Welcome to Video site. Federal investigators have also filed a court complaint to recover 24 cryptocurrency accounts tied to the site.

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