U.S. intelligence agencies have a direct tap into the servers of the U.S.'s largest Internet companies where agents can troll for suspicious activity, sources confirmed to NBC News on Thursday.

A government program is examining suspicious email and Internet traffic. According to The Washington Post, it allows the NSA and the FBI to tap directly into computer servers at some of the largest Internet service providers. NBC's Pete Williams reports.

The highly classified program, designed to look at international communications and run by the National Security Agency and the FBI, can peek at video, audio, photos, emails and other documents, including connection logs that let the government track people, according to the sources, who spoke with NBC News on condition of anonymity.

Intelligence officials disputed reports that the program was engaged in "data mining" and instead described the activities as "data collection." It was unclear what the distinction is in practical terms.

The program, code-named PRISM, was first publicly exposed Thursday evening by The Washington Post and The Guardian.

According to the Post, which reported that it had obtained an internal NSA presentation on the PRISM operation, the tool was so successful that it was the top contributor to President Barack Obama's daily intelligency brief — with 1,477 articles last year.

The participating technology companies were a virtual "Who's Who" of Silicon Valley, including Microsoft, Yahoo, Google, Facebook, PalTalk, AOL, Skype, YouTube and Apple, the Post said.

Companies contacted by NBC denied knowledge of the PRISM operation, which has been described as a "partnership" with the technology industry.

"Google does not have a 'back door' for the government to access private user data," Google spokesman Chris Gaither said.

"We do not provide any government organization with direct access to Facebook servers," Facebook's chief security officer, Joe Sullivan, said in a statement.

"We have never heard of PRISM," an Apple spokesman told CNBC. "We do not provide any government agency with direct access to our servers, and any government agency requesting customer data must get a court order."

Microsoft and Yahoo also denied to NBC News knowledge of the program, saying they only comply with legal requests for information on specific individuals.

According to the NBC News sources, PRISM works in tandem with another program, code-named BLARNEY, which collects "metadata" — Internet addresses, device signatures and such — as the data streams past intersections on the Internet backbone.

Information from the enormous collection of U.S. telephone calls and their durations has been housed in National Security Agency computers for the past seven years. NBC's Andrea Mitchell reports.

Disclosure of the PRISM program comes a day after the Guardian reported that the U.S. government had compelled telephone giant Verizon to turn over phone records of millions of U.S. customers.

Intelligence officials were reeling over the leak about PRISM on Thursday night, sources told NBC News.

The groundwork for doing such widespread monitoring appeared to be first laid in 2007 in the hastily passed "Protect America Act."

Thursday's revelations are believed to be the first publicly released results of the law.

Kurt Upsahl, a senior staff attorney for the Electronic Frontier Foundation, said the digital civil rights organization "has been saying for some time that there has been a warrantless surveillance program going on" for the collection of electronic content.

"It allegedly has the cooperation of nine very prominent Internet companies, from which we're seeing a slew of denials," he told NBC News. "Denials that are designed to leave the impression that the companies are not participating."

At "minimum," he said, "Congress should start holding some hearings and get to the bottom of what's going on."

The American Civil Liberties Union also was quick to offer its concerns about what was reportedly a court-approved program that had the consent of Congress.

"These revelations are a reminder that Congress has given the government far too much power to invade individual privacy, that existing civil liberties safeguards are grossly inadequate," Jameel Jaffer, the ACLU's deputy legal director, said in a statement, adding that "powers exercised entirely in secret, without public accountability of any kind, will certainly be abused."

However, James R. Clapper, Obama's director of national intelligence, said in a statement that the Post and The Guardian articles contained "numerous inaccuracies" in reference to Section 702 of the Foreign Intelligence Surveillance Act.

Section 702, he said, is designed to help acquire foreign intelligence for non-U.S. persons outside the country and can't be used to target Americans or others within the U.S.

He said all activities authorized by Section 702 are subject to oversight by a special court, the executive branch and Congress and must follow "extensive procedures" to "ensure only non-U.S. persons outside the U.S. are targeted."

Clapper stressed that the program "does not allow the Government to listen in on anyone's phone calls" and that "the information acquired does not include the content of any communications or the identity of any subscriber."

"The unauthorized disclosure of information about this important and entirely legal program is reprehensible and risks important protections for the security of Americans," he said.

Pete Williams, Suzanne Choney and Bob Sullivan of NBC News contributed to this report.

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