The highly classified program, code-named PRISM, has not been disclosed publicly before. Its establishment in 2007 and six years of exponential growth took place beneath the surface of a roiling debate over the boundaries of surveillance and privacy. Even late last year, when critics of the foreign intelligence statute argued for changes, the only members of Congress who know about PRISM were bound by oaths of office to hold their tongues.

An internal presentation on the Silicon Valley operation, intended for senior analysts in the NSA’s Signals Intelligence Directorate, described the new tool as the most prolific contributor to the President’s Daily Brief, which cited PRISM data in 1,477 articles last year. According to the briefing slides, obtained by The Washington Post, “NSA reporting increasingly relies on PRISM” as its leading source of raw material, accounting for nearly 1 in 7 intelligence reports.

That is a remarkable figure in an agency that measures annual intake in the trillions of communications. It is all the more striking because the NSA, whose lawful mission is foreign intelligence, is reaching deep inside the machinery of American companies that host hundreds of millions of American-held accounts on American soil.

The technology companies, which participate knowingly in PRISM operations, include most of the dominant global players of Silicon Valley. They are listed on a roster that bears their logos in order of entry into the program: “Microsoft, Yahoo, Google, Facebook, PalTalk, AOL, Skype, YouTube, Apple.” PalTalk, although much smaller, has hosted significant traffic during the Arab Spring and in the ongoing Syrian civil war.

Dropbox , the cloud storage and synchronization service, is described as “coming soon.”

Government officials declined to comment for this story.

PRISM is an heir, in one sense, to a history of intelligence alliances with as many as 100 trusted U.S. companies since the 1970s. The NSA calls these Special Source Operations, and PRISM falls under that rubric.

The Silicon Valley operation works alongside a parallel program, code-named BLARNEY, that gathers up “metadata” — address packets, device signatures and the like — as it streams past choke points along the backbone of the Internet. BLARNEY’s top-secret program summary, set down alongside a cartoon insignia of a shamrock and a leprechaun hat, describes it as “an ongoing collection program that leverages IC [intelligence community] and commercial partnerships to gain access and exploit foreign intelligence obtained from global networks.”

But the PRISM program appears more nearly to resemble the most controversial of the warrantless surveillance orders issued by President George W. Bush after the al-Qaida attacks of Sept. 11, 2001. Its history, in which President Barack Obama presided over “exponential growth” in a program that candidate Obama criticized, shows how fundamentally surveillance law and practice have shifted away from individual suspicion in favor of systematic, mass collection techniques.

The PRISM program is not a dragnet, exactly. From inside a company’s data stream the NSA is capable of pulling out anything it likes, but under current rules the agency does not try to collect it all.

Analysts who use the system from a Web portal at the NSA headquarters in Fort Meade, Md. key in “selectors,” or search terms, that are designed to produce at least 51 percent confidence in a target’s “foreignness.” That is not a very stringent test. Training materials obtained by the Post instruct new analysts to submit accidentally collected U.S. content for a quarterly report, “but it’s nothing to worry about.”

Even when the system works just as advertised, with no American singled out for targeting, the NSA routinely collects a great deal of American content. That is described as “incidental,” and it is inherent in contact chaining, one of the basic tools of the trade. To collect on a suspected spy or foreign terrorist means, at minimum, that everyone in the suspect’s inbox or outbox is swept in. Intelligence analysts are typically taught to chain through contacts two “hops” out from their target, which increases “incidental collection” exponentially. The same math explains the aphorism, from the John Guare play, that no one is more than “six degrees of separation” from Kevin Bacon.

Formally, in exchange for immunity from lawsuits, companies like Yahoo and AOL are obliged accept a “directive” from the attorney general and the director of national intelligence to open their servers to the FBI’s Data Intercept Technology Unit, which handles liaison to U.S. companies from the NSA. In 2008, Congress gave the Justice Department authority to for a secret order from the Foreign Surveillance Intelligence Court to compel a reluctant company “to comply.”

In practice, there is room for a company to maneuver, delay or resist. When a clandestine intelligence program meets a highly regulated industry, said a lawyer with experience in bridging the gaps, neither side wants to risk a public fight. The engineering problems so immense, in systems of such complexity and frequent change, that the FBI and NSA would be hard pressed to build in back doors without active help from each company.

Apple demonstrated that resistance is possible, for reasons unknown, when it held out for more than five years after Microsoft became PRISM’s first corporate partner in May 2007. Twitter, which has cultivated a reputation for aggressive defense of its users’ privacy, is still conspicuous by its absence from the list of “private sector partners.”

“Google cares deeply about the security of our users’ data,” a company spokesman said. “We disclose user data to government in accordance with the law, and we review all such requests carefully. From time to time, people allege that we have created a government ‘back door’ into our systems, but Google does not have a ‘back door’ for the government to access private user data.”

Like market researchers, but with far more privileged access, collection managers in the NSA’s Special Source Operations group, which oversees the PRISM program, are drawn to the wealth of information about their subjects in online accounts. For much the same reason, civil libertarians and some ordinary users may be troubled by the menu available to analysts who hold the required clearances to “task” the PRISM system.

There has been “continued exponential growth in tasking to Facebook and Skype,” according to the 41 PRISM slides. With a few clicks and an affirmation that the subject is believed to be engaged in terrorism, espionage or nuclear proliferation, an

analyst obtains full access to Facebook’s “extensive search and surveillance capabilities against the variety of online social networking services.”

According to a separate “User’s Guide for PRISM Skype Collection,” that service can be monitored for audio when one end of the call is a conventional telephone and for any combination of “audio, video, chat, and file transfers” when Skype users connect by computer alone. Google’s offerings include Gmail, voice and video chat, Google Drive files, photo libraries, and live surveillance of search terms.

Firsthand experience with these systems, and horror at their capabilities, is what drove a career intelligence officer to provide PowerPoint slides about PRISM and supporting materials to The Washington Post in order to expose what he believes to be a gross intrusion on privacy. “They quite literally can watch your ideas form as you type,” the officer said.

tinyurl.com/PostNSAslides

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