Revealed: the top secret rules that allow NSA to use US data without a warrant

> Retain and make use of "inadvertently acquired" domestic communications if they contain usable intelligence, information on criminal activity, threat of harm to people or property, are encrypted, or are believed to contain any information relevant to cybersecurity

So if they "inadvertently" discover you're breaking a law during their mass surveillance, they can forward it to the relevant authorities.

> Access the content of communications gathered from "U.S. based machine[s]" or phone numbers in order to establish if targets are located in the US, for the purposes of ceasing further surveillance

Brilliant. In order to prevent spying on citizens, they spy on citizens to make sure they're citizens who can't be spied on.