United States. National Security Agency

In a new book, Dark Mirror, Barton Gellman writes about his relationship with Edward Snowden and the high-stakes reporting that ultimately garnered him, Poitras and Greenwald a Pulitzer Prize.

In 2013, Edward Snowden was an IT systems expert working under contract for the National Security Agency when he traveled to Hong Kong to provide three journalists with thousands of top-secret documents about U.S. intelligence agencies' surveillance of American citizens.

NY Times cybersecurity correspondent Nicole Perlroth says hacking tools developed by the NSA were stolen, posted online and are now being used in cyberattacks, including one on the city of Baltimore.

In the book @War, Shane Harris reports that U.S. intelligence agencies, sometimes aided by corporations, are trying to dominate cyberspace. It's "changing the Internet in fundamental ways," he says.

Laura Poitras' new film isn't artfully shaped like her other documentaries. But she captures scenes as history is being made — and it will make you look both ways when you're on the street.

PBS looks at the origins of the agency's surveillance program and the extraordinary steps top government officials took to give it legal cover and keep it hidden.

What motivated the former NSA contractor to divulge careful guarded NSA secrets? A new Vanity Fair article takes a look back at the "kid from the Maryland suburbs."

The NSA managed to penetrate the networks of the giant Chinese telecommunications firm Huawei, documents show. Journalist David Sanger says cyber-espionage is an "entirely new field of conflict."

Before whistle-blower Edward Snowden became a household name, he was an anonymous source. The Washington Post's Barton Gellman recounts how he began corresponding with Snowden and the process of reporting on the government's Internet data mining program.