Law enforcement officials said on Wednesday they had arrested hundreds of people worldwide after knocking out a South Korea-based dark web child pornography site that sold videos for digital cash.

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.

Called Welcome To Video, the site relied on the cryptocurrency bitcoin to sell access to 250,000 videos depicting child sexual abuse, authorities said, including footage of extremely young children being raped.