Q and A: Behind the NSA mining program

Q: What information is being obtained?

A: The order called it "metadata" that consisted of telephone numbers and the times and duration of calls, but not the contents of the phones calls or the names and addresses of those who owned the phones. And Director of National Intelligence James Clapper Jr. on Saturday described another top-secret surveillance program, called PRISM, as limited in scope. The program has enabled national security officials to collect e-mail, videos, documents and other material from at least nine U.S. companies over six years, including Google, Microsoft and Apple, according to documents obtained by the Washington Post.

Clapper said the program is "an internal government computer system used to facilitate the government's statutorily authorized collection of foreign intelligence information from electronic communication service providers under court supervision. PRISM is not an undisclosed collection or data mining program."

Q: How does the government get access to the data?

A: Through a court order and by relying on a provision in the USA Patriot Act.

Q: Who makes the decisions on these requests?

A: The Foreign Intelligence Surveillance Court, whose judges operate in secret. They are appointed by Chief Justice John Roberts.

A: The Fourth Amendment forbids "unreasonable searches" by the government, but the Supreme Court has drawn a sharp distinction between what is truly private and what is not. When people talk on the phone, that is a private conversation, the court said, and it is protected by the Constitution. So, before police can "wiretap" a phone call, they must seek a search warrant from a judge. This requires showing they have "probable cause" to believe a crime is in progress. But in the 1970s, the court said business records, tax records and phone records are not truly private. Because such records are not protected under the 4th Amendment, a police official or FBI agent may obtain them by sending an order to a business saying they are needed for an investigation.

Q: Is there any legal limit on what records the government may secretly obtain?

A: Before this week, many had assumed the law limited the government to obtaining only records that were "relevant to an authorized investigation." These words from the Patriot Act were read to mean officials were tracking certain people because they were suspected of involvement in terrorism. But the current order made no mention of an actual investigation. On Capitol Hill, senators who serve on the Intelligence Committee said this has gone on since at least 2006. Some experts say the Justice Department must take the view that having access to the entire database of phone calls is "relevant" to investigating terrorism plots.

Q: How has this surveillance program remained secret?

A: Lawmakers voted to keep it secret from the American people. The Senate defeated amendments in 2010 and 2011 that would have required the Justice Department to explain its view that the law permits the government to secretly obtain all U.S. phone records. President Obama's Justice Department has refused to release its legal explanations. And the high court has tossed out lawsuits from civil libertarians on the grounds that none of them could prove they were secretly wiretapped.