Federal prosecutors charged WikiLeaks founder Julian Assange with espionage Thursday for conspiring to reveal national security secrets in what they described as one of the largest compromises of classified information in U.S. history.

The Justice Department revealed 18 charges against Assange. They include allegations that he aided and abetted former Army intelligence analyst Chelsea Manning’s efforts to leak classified documents to the anti-secrecy group and committed a crime by publishing them on the internet.

“This release made our adversaries stronger and more knowledgeable, and the United States less secure,” said John Demers, assistant attorney general for national security.