Prosecutors in Germany claim to have shut down one of the world's largest darknet sites for child pornography.
More than 400,000 registered members used the "Boystown" platform, according to authorities.
Pedophiles from all over the world used the site to share and display pornography involving children and toddlers, the majority of whom were boys, they added.
The photographs and video content included "videos of the most serious sexual abuse of toddlers," according to the investigators.
In a joint statement with the Federal Criminal Police Office, Frankfurt prosecutors said that three German perpetrators, said to be the platform's managers, were arrested along with a German user in mid-April. In Paraguay, one of the three key suspects was apprehended.
In connection with the investigation, they also searched seven buildings in Germany.
International police activity is underway.
The investigation was conducted by German police in collaboration with Europol and law enforcement authorities from the Netherlands, Sweden, Australia, the United States, and Canada.
A 40-year-old Paderborn man, a 49-year-old Munich man, and a 58-year-old northern German man who had lived in Paraguay for several years were the three key suspects.
According to the prosecutors' argument, they served as site managers and provided participants tips about how to avoid law enforcement while using the website for illicit child pornography.
A fourth defendant, a 64-year-old Hamburger, is suspected of being one of the platform's most prolific users, having reportedly posted over 3,500 times.
The defendant who was arrested in Paraguay has been extradited to Germany.
In accordance with German privacy laws, no names were given. The web portal was shut down after the raids in mid-April.