A federal appeals court on Tuesday revived a high-profile challenge to the National Security Agency's warrantless surveillance of internet communications. The ruling ... increases the chances that the Supreme Court may someday scrutinize whether the N.S.A.'s so-called upstream system for internet surveillance complies with Fourth Amendment privacy rights. The ruling reversed a Federal District Court judge's decision to throw out the case. The district judge had ruled that the plaintiffs - including the Wikimedia Foundation - lacked standing to sue because they could not prove that their messages had been intercepted. Because of how the internet works, surveillance of communications crossing network switches is different from traditional circuit-based phone wiretapping. While the government can target a specific phone call without touching anyone else's communications, it cannot simply intercept a surveillance target's email. Instead ... to find such emails it is necessary first to systematically copy data packets crossing a network switch and sift them in search of components from any messages involving a target. Documents provided by [Edward] Snowden and declassified by the government have shown that this system works through equipment installed at the facilities of companies, like AT&T, that [connect] the American internet to the rest of the world. Privacy advocates contend that the initial copying and searching of all those data packets ... violates Fourth Amendment protections against government search and seizure.