18 U.S. Code §793

Citation
18 U.S. Code § 793 &mdash; Gathering, transmitting or losing defense information (https://www.law.cornell.edu/uscode/text/18/793 full-text]).

Overview
It is a federal crime, punishable by imprisonment for up to 10 years, to disclose national defense information to someone who is not entitled to receive it. At least one court has indicated that "national defense information" consists of "all matters that directly or may reasonably be connected with the defense of the United States against any of its enemies" that are not publicly known.

Almost every press leak case involves a conviction for, or at least charges of, a violation of Section 793 of the Espionage Act of 1917. Perhaps the earliest and most famous involves Daniel Ellsberg. Ellsberg was a RAND Corp. employee who in 1971 supplied the press with the "Pentagon Papers," a classified study of U.S. decision making associated with the growingly unpopular war in Vietnam. His trial on espionage charges ended in dismissal on grounds unrelated to the scope of Section 793.