German police have busted a child sex abuse site on the dark web where images and videos were exchanged.
The secret Elysium website had 87,000 members and was launched on the internet in December, prosecutors say.
The suspected ringleader, a 39-year-old man, was arrested in the state of Hesse. The forum was also used to make appointments to abuse children.
Police seized the website's server. They found that toddlers were among the children sexually abused, reports say.
The chief suspect was arrested at his home in the Limburg-Weilburg area north of Frankfurt on 12 June.
He has been linked not only to spreading videos and images of child sex abuse but is also suspected of carrying out acts of serious sexual abuse.
Several suspected users of the site have been arrested in Germany and Austria.
Three were held in Germany and another 14 were detained in Austria, according to local reports. Prosecutors were due to give further details on Friday.
The website only appeared on the dark web at the end of last year but attracted tens of thousands in a matter of months.
Sites on the dark web are not visible through normal search engines, and while there are many legitimate uses for it, it has become a magnet for online criminal activity.