A dual citizen of Ireland and the US has pleaded guilty in court in Maryland to conspiracy to advertise child pornography.
As part of a plea agreement, 33-year-old Eric Eoin Marques from Dublin admitted that between 24 July 2008 and 29 July 2013 he conspired to advertise child pornography by operating an anonymous web hosting service.
He will be sentenced on 11 May.
"Child pornography is created by documenting the sexual abuse of children," said US Attorney Robert K Hur of the District of Maryland.
"This is an egregious case where one individual facilitated the abuse of more than a million new child victims and attempted to keep the abuse hidden on the dark web.
"We must do everything we can to bring individuals like Marques to justice in order to keep our children safe."
According to court documents, between 24 July 2008 and 29 July 2013, Marques operated a free anonymous hosting service located on the "dark web," an area of the Internet that is only accessible by means of special software, allowing users and website operators to remain anonymous or untraceable.
The service hosted websites that allowed users to view and share images documenting the sexual abuse of children.
The investigation revealed that the hosting service contained over 8.5 million images of child exploitation material and over 1.97 million of these images and/or videos involved victims that were not known by law enforcement.
US authorities say they conducted the investigation with significant assistance from the Legal Attaché London Office, An Garda Síochána and EUROPOL.