Authorities have shut down a massive underground child pornography network, arresting 337 alleged users in the process, the Department of Justice announced on Wednesday. The mastermind, a South Korean man named Jong Wo Son, ran the Tor hidden service from a server in his bedroom, according to authorities.

The feds say the site hosted 200,000 video files. Users who uploaded videos to the site were rewarded with free access to videos uploaded by others. Users could also purchase access to the videos using bitcoin.

A notice on the upload page stated "do not upload adult porn." A search page listed popular search terms on the site including "PTHC" ("preteen hardcore") and "%4yo."

Poor opsec aided the mastermind’s capture

In theory, Tor's onion-routing technology makes it possible to run an untraceable network. But doing so requires owners to be meticulous about covering their own tracks. Son apparently failed to do this. Authorities say they found the actual IP address of his server by looking at the site's source code.

The indictment, obtained by Ars alum Cyrus Farivar, suggests that Son did a poor job of covering his tracks when he accepted bitcoins, too. Undercover agents made several bitcoin payments to addresses associated with the site. Those payments were then transferred to an address associated with a bitcoin exchange.

According to the indictment, that exchange had a signature card on file that listed the defendant's name, cell phone number, and email address. The law in the US and some other countries requires exchanges to collect this kind of identifying information.

This contrasts with more sophisticated dark-Web purveyors like Ross Ulbricht, the proprietor of the now-shuttered drug emporium The Silk Road. As we reported in 2013, Ulbricht "ran a program called a tumbler to route incoming Bitcoin payments through a complicated series of dummy transactions, so as to make them infeasible to trace through the public Bitcoin blockchain."

Ulbricht also enhanced his privacy by keeping most of his earnings in bitcoin. In contrast, Son converted his holdings to conventional currency, which meant interacting with conventional payment services that required his identity. The feds eventually caught Ulbricht, but it took months of careful sleuthing. Catching Son was comparatively trivial.

A multiyear project

The indictment was dated May 3, 2018. The Justice Department says Son has already been convicted in South Korean courts. The authorities seized his servers, which contained 8 terabytes of illicit material.

Presumably the reason the US government waited so long to announce the bust was to provide enough time to round up the site's users.

The government says 337 defendants residing in 23 states, the District of Columbia, South Korea, and 10 other countries around the world have been arrested and charged for crimes relating to the site. Several defendants have already been convicted, according to the government.

The feds say they also aided in the rescue of 23 child victims who were still being abused by site users. Two suspects committed suicide after search warrants were executed against them, the authorities say.