The Department of Defense is blocking online access to news reports about classified National Security Agency documents made public by Edward Snowden. The blackout affects all of the department's computers and is part of a department-wide directive.

"Any website that runs information that the Department of Defense still considers classified" is affected, Pentagon spokesman Lt. Col. Damien Pickart told U.S. News in a phone interview.

According to Pickart, news websites that re-report information first published by The Guardian or other primary sources are also affected.

"If that particular website runs an article that our filters determine has classified information... the particular content on that website will remain inaccessible," he said.

The Defense Department's blackout of NSA references will affect millions of computers. (Vyacheslav Oseledko/AFP/Getty Images)

Pickart said the blackout affects "millions" of computers on "all Department of Defense networks and systems."

The spokesman told U.S. News that original reports about the leaks may be specifically targeted for the blackout. He admitted that "automated filters are never perfect," and some reports may slip through the cyber blockade.

Pickart declined to identify the source of the military-wide dictate.

"This is the same as what we did during the WikiLeaks situation," he said. Personal computers used by military employees aren't affected, Pickart said. One of the primary rationales for the blackout is money: "it's costly, it takes a lot of time" to scrub computers of unauthorized, classified material viewed by servicemen while reading online news reports, Pickart said.

"Should any website choose to post information the department deems classified, that particular content on the website will be filtered and remain inaccessible from DoD networks so long as it remains classified," Pickart reiterated in an emailed statement.

"The department does not determine what sites its personnel can choose to visit while on a DoD system, but instead relies on automated filters that restrict access based on content concerns or malware threats. The DoD is also not going to block websites from the American public in general, and to do so would violate our highest-held principle of upholding and defending the Constitution and respecting civil liberties and privacy."

The Monterey Herald reported Thursday that the Army was restricting access to The Guardian's website. A spokesman for the Army Network Enterprise Technology Command confirmed that the policy affected The Guardian, but the scope of the military's blackout wasn't immediately clear.