Jennifer K. Elsea, Criminal Prohibitions on the Publication of Classified Defense Information (CRS Report R41404) (Jan. 31, 2013) (full-text).
This report identifies some criminal statutes that may apply to the online publication of classified defense documents and diplomatic cables. It notes that these statutes have been used almost exclusively to prosecute individuals with access to classified information (and a corresponding obligation to protect it) who make it available to foreign agents, or to foreign agents who obtain classified information unlawfully while present in the United States.
Leaks of classified information to the press have only rarely been punished as crimes, and there are no cases in which a publisher of information obtained through unauthorized disclosure by a government employee has been prosecuted for publishing it. There may be First Amendment implications that would make such a prosecution difficult, not to mention political ramifications based on concerns about government censorship.
To the extent that the investigation implicates any foreign nationals whose conduct occurred entirely overseas, any resulting prosecution may carry foreign policy implications related to the exercise of extraterritorial jurisdiction and whether suspected persons may be extradited to the United States under applicable treaty provisions.
The report discusses the statutory prohibitions that may be implicated, including the Espionage Act of 1917; the extraterritorial application of such statutes; and the First Amendment implications related to such prosecutions against domestic or foreign media organizations and associated individuals.