Officials placed the forums in former Soviet bloc countries where the upper echelon members of the organization resided. It was estimated that, in July 2011, there were more than 5,500 members.

Authorities determined members of the organization had different roles, including moderators who directed other members in carrying out activities; reviewers who examined and tested products, services, and contraband; vendors who advertised and sold products, services and contraband; and, the members themselves. Members were required to successfully complete a number of security features designed to protect the organization from infiltration by law enforcement or members of rival criminal organizations.

Officials said Litvinenko's extradition is the result of close coordination among ICE Homeland Security Investigation's attaché office in Vienna, Austria; the U.S. Secret Service attaché office in Rome; the U.S. State Department Diplomatic Security Service; the U.S. Department of Justice's Office of International Affairs; Interpol; the Croatian Ministries of Justice and the Interior; and the Croatian State Prosecutor's Office.

Originally arrested by Croatian authorities in August 2012 based upon the U.S. charges, a Croatian higher court cleared the way for Litvinenko's extradition last month, the authorities said.

"We owe a tremendous debt to the Croatian authorities for the extraordinary assistance they provided in this case," said HSI Executive Associate Director James Dinkins. "It's another powerful reminder that we won't allow our borders to be barriers to bringing international fugitives to justice."

"This operation demonstrates there is no such thing as anonymity in the cyber world. Our success in this operation and other similar investigations is a result of our close work with our network of law enforcement partners," said Secret Service Assistant Director Paul Morrissey of the Office of Investigations.