The U.S. National Security Agency has worked with companies to weaken encryption products at the same time it infiltrated firms to gain access to sensitive systems, according to a purportedly leaked classified document outlined in an article on The Intercept.

The document, allegedly leaked by former NSA contractor Edward Snowden, appears to be a highly classified summary intended for a very small group of vetted national security officials according to details included in The Intercept article, which was published this weekend. The document outlines six programs at the core of the NSA's mission, collected under the name Sentry Eagle.

The Intercept claims the document states "The facts contained in [the Sentry Eagle] program constitute a combination of the greatest number of highly sensitive facts related to NSA/CSS’s overall cryptologic mission."

The programs include computer network exploitation and espionage, computer network defense, computer network attack, the NSA's work with other intelligence agencies, its work with private companies, and the agency's original mission of breaking encryption codes and systems.

The NSA has infiltrated a number of critical companies as part of its strategy of target exploitation, or TAREX. While some of the companies are in nations the United States considers adversaries, such as China, others appear to be in allied nations, such as South Korea and Germany, according to the article. The document suggests that agents exist inside American companies as well, according to the article.

"The briefing document states that among Sentry Eagle’s most closely guarded components are 'facts related to NSA personnel (under cover), operational meetings, specific operations, specific technology, specific locations and covert communications related to SIGINT enabling with specific commercial entities (A/B/C)," the article states, adding that "A/B/C" is a placeholder typically used to refer to American companies.

Since Snowden first leaked highly classified documents from the National Security Agency in June 2013, he's fed a steady trickle of classified information to journalist Glenn Greenwald, documentarian Laura Poitras, and major news organizations. These documents have outlined the depth and breadth of spying by, not just the National Security Agency, but other nations' intelligence groups as well.

The latest leak appears timed to coincide with the premier of Poitras' documentary on Snowden at the New York Film Festival.

The Intercept article cites the document's warning that "unauthorized disclosure ... will cause exceptionally grave damage to U.S. national security."

The NSA provided only a brief response to the publication, stating in part: “It should come as no surprise that NSA conducts targeted operations to counter increasingly agile adversaries."