Canadians are among the 338 people charged as part of a global criminal investigation into a child pornography website that sold videos using bitcoin digital currency, U.S. law enforcement officials said Wednesday. 

The website called Welcome To Video was taken offline in March 2018 and contained over 250,000 unique videos, the U.S. Justice Department said.

Officials from the United States, Britain and South Korea described the network as one of the largest child pornography operations they had encountered to date.

Law enforcement authorities said they have arrested and charged subjects in the U.S., the United Kingdom, South Korea, Germany, Saudi Arabia, United Arab Emirates, the Czech Republic, Canada, Ireland, Spain, Brazil and Australia. The Justice Department did not specify the number of people from each country who were charged. 

The site’s operator, a South Korean named Jong Woo-son, and 337 users in 12 different countries, have been charged so far, authorities said.

Jong, currently serving an 18-month sentence in South Korea, was also indicted on federal charges in Washington.

Several other people charged in the case have already been convicted and are serving prison sentences of up to 15 years, the Justice Department said.

The investigation has led to the rescue of at least 23 underage victims in the U.S., Britain and Spain who were being actively abused by users of the site. Many children in the videos have not yet been identified.

Welcome to Video is one of the first websites to monetize child pornography using bitcoin, which allows users to hide their identities during financial transactions, the authorities said.

Users were able to redeem the digital currency in return for points that they could spend downloading videos or buying all-you-can watch VIP accounts. Points could also be earned by uploading new child pornography.

The Justice Department said the site collected at least $370,000 worth of bitcoin before it was taken down in March 2018 and that the currency was laundered through three unnamed digital currency exchanges.