Quite a few high-profile instances of leaks, breaches, infractions, cracks and “extreme carelessness in the handling of” classified information have been in the news over the last few years, and while folks like to talk a lot of fluff about whether this or that instance was truly vile or truly virtuous, I’ve never actually seen anyone reference the underlying rules regarding defense information.
So here it is: 18 U.S. Code § 793
Cornell Law has the text posted here as well.