While the data provided varies according to the online provider, it could include email, chat services, videos, photos, stored data, file transfers, video conferencing and logins - according to an apparently highly classified document describing the National Security Agency program called Prism.
The program is authorized under law and was recently reauthorized by Congress, said the senior official, who said it minimized the collection and retention of information "incidentally acquired" about Americans and permanent residents. Several of the Internet companies issued statements strongly denying knowledge of or participation in the program.
"The law does not allow the targeting of any U.S. citizen or of any person located within the United States," said the official, who insisted on anonymity to discuss a highly classified program. "Information collected under this program is among the most important and valuable intelligence information we collect and is used to protect our nation from a wide variety of threats."
But the disclosure of the documents by U.S. and British newspapers came just hours after government officials acknowledged a separate seven-year effort to sweep up records of telephone calls inside the United States. Together, the unfolding disclosures opened an extraordinary window into the growth of government surveillance that began under the Bush administration after the Sept. 11 terrorist attacks and has clearly been embraced and even expanded under the Obama administration.
The revelations, in rapid succession, also suggested that someone with access to high-level intelligence secrets had decided to unveil them in the midst of furor over leak investigations. Both were reported by Britain's Guardian newspaper, while The Washington Post, relying upon the same presentation, simultaneously reported the Internet company tapping. The Post said a disenchanted intelligence official had provided it with the documents to expose government overreach.
Before the disclosure of the alleged Internet company surveillance program late Thursday, the White House and congressional leaders defended the phone program, saying it was legal and necessary to protect national security.
Josh Earnest, a White House spokesman, told reporters aboard Air Force One that the kind of surveillance at issue "has been a critical tool in protecting the nation from terror threats as it allows counterterrorism personnel to discover whether known or suspected terrorists have been in contact with other persons who may be engaged in terrorist activities, particularly people located inside the United States."
He added: "The president welcomes a discussion of the trade-offs between security and civil liberties."
The Guardian and The Post posted several slides from the 41-page presentation about the Internet program, listing the companies involved - which included Yahoo, Microsoft, Paytalk, AOL, Skype and YouTube - and the dates they joined the program, as well as listing the types of information collected under the program.
The NSA and other government agencies declined to comment about the disclosures. The possibility of a broad government sweep of domestic telephone data in pursuit of potential terrorists has long been suspected by civil liberties advocates and even hinted at by members of Congress. But the public disclosure of a secret court order confirmed it in a more concrete way than ever before.
The reports came as President Barack Obama was traveling to meet President Xi Jinping of China at an estate in Southern California, a meeting intended to address among other things complaints about Chinese cyberattacks and spying. Now that conversation will take place amid discussion of America's own vast surveillance operations on its own citizens.
But while the administration and lawmakers who supported the telephone records program emphasized that all three branches of government had signed off on it, Anthony Romero of the American Civil Liberties Union denounced the surveillance as an infringement of fundamental individual liberties, no matter how many parts of the government approved of it.
"A pox on all the three houses of government," Romero said. "On Congress, for legislating such powers, on the FISA court for being such a paper tiger and rubber stamp, and on the Obama administration for not being true to its values."
Others raised concerns about whether the telephone program was effective.
Word of the program emerged when The Guardian posted an April order from the secret foreign intelligence court directing a subsidiary of Verizon Communications to give the NSA "on an ongoing daily basis" until July logs of communications "between the United States and abroad" or "wholly within the United States, including local telephone calls."
On Thursday, Sens. Dianne Feinstein of California and Saxby Chambliss of Georgia, the top Democrat and top Republican on the Intelligence Committee, said the court order appeared to be a routine reauthorization as part of a broader program that lawmakers had long known about and supported.
"As far as I know, this is an exact three-month renewal of what has been the case for the past seven years," Feinstein said, adding that it was carried out by the Foreign Intelligence Surveillance Court "under the business records section of the Patriot Act."
"Therefore, it is lawful," she said. "It has been briefed to Congress."
While refusing to confirm or to directly comment on the reported court order, Verizon, in an internal email to employees, defended its release of calling information to the NSA. Randy Milch, an executive vice president and general counsel, wrote that "the law authorizes the federal courts to order a company to provide information in certain circumstances, and if Verizon were to receive such an order, we would be required to comply."
Sprint, T-Mobile and CenturyLink, the other major landline and wireless phone companies in the United States, all declined to say Thursday whether they were or had been under a similar court order.
Lawmakers and administration officials who support the phone program defended it in part by noting that it was only for "metadata" - like logs of calls sent and received - and did not involve listening in on people's conversations.
But the alleged Internet company program reported on Thursday did appear to involve eavesdropping on the contents of communications. The Guardian reported that one slide on the presentation said the operations had "assistance of communications providers in the U.S."
It was not immediately clear what the legal basis for such a program could be. Several of the companies named in the reports - including Google, Facebook and Apple - issued strong denials that any such program existed. A spokeswoman for Google, for example, said the company had "no knowledge" of the Prism program.
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"Google cares deeply about the security of our users' data," the company said in a statement. "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 'backdoor' into our systems, but Google does not have a 'backdoor' for the government to access private user data."
Apple also denied knowing about any such program.
"We have never heard of Prism," said Steve Dowling, an Apple spokesman. "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."
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While murky questions remained about the alleged Internet company program, the confirmation of the calling log program solved a mystery that has puzzled national security legal policy observers in Washington for years: why a handful of Democrats on the Senate Intelligence Committee were raising cryptic alarms about Section 215 of the Patriot Act, the law Congress enacted after the 9/11 attacks.
Section 215 made it easier for the government to obtain a secret order for business records, so long as they were deemed relevant to a national security administration.
Section 215 is among the sections of the Patriot Act that have periodically come up for renewal. Since around 2009, a handful of Democratic senators briefed on the program - including Ron Wyden of Oregon - have sought to tighten that standard to require a specific nexus to terrorism before someone's records could be obtained, while warning that the statute was being interpreted in an alarming way that they could not detail because it was classified.
On Thursday, Wyden confirmed that the program was what he and others have been expressing concern about. He said he hoped the disclosure would "force a real debate" about whether such "sweeping, dragnet surveillance" should be permitted - or is even effective.
"I believe that when law-abiding Americans call their friends, who they call, when they call and where they call from is private information," he said. "Collecting this data about every single phone call that every American makes every day would be a massive invasion of Americans' privacy."
But just as efforts by Wyden and fellow skeptics, including Sens. Richard J. Durbin of Illinois and Mark Udall of Colorado, to tighten standards on whose communications logs could be obtained under the Patriot Act have repeatedly failed, their criticism was engulfed in a clamor of broad, bipartisan support for the program.
"If we don't do it," said Sen. Lindsey Graham, R-S.C., "we're crazy."
And Rep. Mike Rogers, R-Mich., the chairman of the House Intelligence Committee, claimed in a news conference that the program helped stop a significant domestic terrorist attack in the United States in the last few years. He gave no details.
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That assertion might come under scrutiny in the days ahead. In March 2012, Wyden and Udall said in a letter to Attorney General Eric H. Holder Jr. that they had "grown increasingly skeptical about the actual value" of the intelligence collection operation that relied upon the Patriot Act and could no longer "take the executive branch's assertions about the importance of this 'operation' at face value."
It has long been known that one aspect of the Bush administration's program of surveillance without court oversight involved vacuuming up communications metadata and mining the database in an effort to identify associates - called a "community of interest" - of a suspected terrorist.
In December 2005, The New York Times revealed the existence of elements of that program, setting off a debate about civil liberties and the rule. But in early 2007, Alberto R. Gonzales, then the attorney general, announced that after months of extensive negotiation, the Foreign Intelligence Surveillance Court had approved "innovative" and "complex" orders bringing the surveillance programs under its authority.One part of that deal, Feinstein's comments suggested, was to begin collecting communications metadata under orders issued by the court under Section 215 of the Patriot Act.