The National Security Agency relies on agents on the ground in China, Germany and South Korea to infiltrate and compromise networks and devices through what's called "physical subversion," according to documents released Friday by The Intercept.

The documents, coming from the trove of information obtained by NSA whistleblower Edward Snowden, describe details relating to various field activities involving computer network attacks - information which is held among the NSA's "core secrets" in what is called Sentry Eagle.

The agency seems to have targeted systems in the global communications industry, and possibly even some American firms, said The Intercept, lending more credibility to what some tech companies have suspected for years: that the NSA is sending agents to infiltrate their private data centers.

While the NSA was long believed to only conduct operations from afar, the newly revealed information contradicts such beliefs and shows that the NSA does have agents working on the ground, "integrated" into operations conducted by the CIA, FBI, and Defense Intelligence Agency, reported The Intercept.

The Intercept wrote:

"Previous disclosures about the NSA's corporate partnerships have focused largely on U.S. companies providing the agency with vast amounts of customer data, including phone records and email traffic. But documents published today by The Intercept suggest that even as the agency uses secret operatives to penetrate them, companies have also cooperated more broadly to undermine the physical infrastructure of the internet than has been previously confirmed."

Also revealed was the fact that the NSA spends "hundreds of millions" of taxpayers' dollars on technology designed to defeat commercial encryption.

Sentry Eagle includes the following six programs: computer network exploitations (Sentry Hawk), computer network defense (Sentry Falcon), cooperation with the CIA and other intelligence agencies (Sentry Osprey), breaking encryption systems (Sentry Raven), computer network operations and attacks (Sentry Condor) and collaborations with private companies (Sentry Owl).

"It should come as no surprise that NSA conducts targeted operations to counter increasingly agile adversaries," the NSA said, citing Presidential Policy Directive 28, which, according to the agency "requires signals intelligence policies and practices to take into account the globalization of trade, investment and information flows, and the commitment to an open, interoperable, and secure global Internet."