His London arrest paved the way for his possible extradition to the United States.
The Justice Department said Assange, 47, was arrested pursuant to the U.S./UK Extradition Treaty, and accused him of involvement in one of the largest compromises of classified information in the history of the United States.
The indictment said that Assange in March 2010 engaged in a conspiracy to assist Manning in cracking a password stored on U.S. Department of Defense computers connected to the Secret Internet Protocol Network (SIPRNet), a U.S. government network used for classified documents and communications.