Washington -- More than 50 members of a child pornography ring who engaged in what authorities describe as "horrific" and "unspeakable" crimes have been arrested for sexually exploiting children from 12 years old to as young as infants.

Top federal law enforcement officials say agents busted the global online pornography ring following an intense international investigation that began in 2009. The ring, based in the United States, reached across five continents and 14 countries.

Seventy-two members of the online site called Dreamboard have been charged in the United States. Officials said 52 of them have been arrested in the U.S. and abroad. The identities of the remaining 20 are unknown at this time.

An additional 10 individuals were arrested abroad on charges from other countries.

"In order to become part of the Dreamboard community, prospective members were required to upload pornography portraying children under 12 years of age or younger," said Attorney General Eric Holder at a Justice Department news conference. "Once given access, the participants had to continually upload images of child sexual abuse in order to maintain membership. The more content they provided, the more content they were allowed to access. Members who created and shared images and videos of themselves molesting children received elevated status and greater access," he said.

What particularly horrified investigators were "super-hardcore" posts that involved adults having violent sexual intercourse with "very young kids" who were being subjected to both physical and sexual abuse.

Holder said, "Some of the children featured in these images and videos were just infants and in many cases, the children being victimized were in obvious and also intentional pain, even in distress and crying, just as the rules for one area of the bulletin board mandated. They had to be in distress and crying."

Homeland Security Secretary Janet Napolitano said, "To give you an example of the scope of this forum, the capture and analysis of the forum revealed that the board may have been the vehicle for the distribution of up to 123 terabytes of child pornography, which is roughly equivalent to nearly 16,000 DVDs. ... Additional media recovered from the targets arrested in the United States alone has been found to contain over one million images of child pornography." Largest US online child pornography bust

About 600 men belonged to the members-only online bulletin board, which has now been taken down. Authorities said the site encouraged and rewarded members who sexually abused young children and made them cry.

"As alleged, Dreamboard had strict rules and a rigid hierarchy. Its membership was tightly controlled by the group's administrators," Assistant Attorney General Lanny Breuer told reporters. "Applicants to the group were required to upload quote nude or hardcore child pornography to become members and members were required to continue posting additional images every 50 days or risk expulsion. Moreover, members could increase their status based on their level of commitment to the enterprise. From member, to VIP, to Super VIP, to the most elite status of all, Super VIP Dot. Only those members who produced their own child pornography could be granted the status of Super VIP Dot," Breuer explained.

"The members of this criminal network shared a demented dream to create the pre-eminent online community for the promotion of child sexual exploitation but for the children they victimized this was nothing short of a nightmare," Holder said.

One Justice Department investigator who asked not to be identified because of the ongoing probe said, "Dozens of young children were directly victimized," some of whom had been identified by agents working the case.

Of the five "administrators" who managed the online community, one was arrested in Canada and another in France. The three others have not yet been identified by agents following the case and remain at large.

"Operation Delego" was spearheaded by agents of Immigration and Customs Enforcement.

John Morton, the head of ICE, said the day marked a law enforcement "success" but was nonetheless a "sad" day because of the nature of the crimes involved.

"There are days in this job where it's hard to separate great success from great sorrow and today is such a day. It's a day of great success because we've brought an end to one of the worst instances of Internet child abuse ICE has ever investigated. ... It's a day of great sorrow because this case is ultimately a tale of the perverse and often violent exploitation of children, very, very young children to satisfy the dark pleasures of a group of adult men," Morton said.

The law enforcement effort has been quietly unfolding in stages during the past few months. Four of the individuals arrested have already pleaded guilty, and all received sentences of more than 20 years in prison. Those sentenced are from Illinois, Alabama, Florida and Kentucky.

Those arrested outside the U.S. were picked up by officials in Canada, Denmark, Ecuador, France, Germany, Hungary, Kenya, the Netherlands, the Philippines, Qatar, Serbia, Sweden and Switzerland.

Holder said, "It's hard for me to imagine that there will ever be a penalty that could appropriately deal with this kind of conduct. Twenty to 30 years that the people have gotten in the past is, from my perspective, barely sufficient to handle what they have done in damaging the lives of these young people."