A newly published court order has confirmed that the government has been routinely mining data about hundreds of millions of U.S. phone calls. The report raised new questions about secret surveillance and unchecked government power.

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.

Q: How does the government get access to this mass of data?

A: Through a court order and by relying on a provision in the Patriot Act. It says the government may obtain business records, phone records or other “tangible things” by going to a special court and “showing that there are reasonable grounds to believe that the tangible things sought are relevant to an authorized investigation.”

Q: Who decides on these requests?

A: The Foreign Intelligence Surveillance Court, whose judges operate in secret. They are appointed by Chief Justice John Roberts. It was Judge Roger Vinson from Florida who approved the order for Verizon phone records.

Q: Is it constitutional for the government to secretly obtain the phone records of ordinary Americans?

A: Probably. 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. So, before police can “wiretap” a phone call, they must persuade a judge to give them a search warrant. 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. These records circulate through offices and through the mail. Because such records are not protected, 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: That is not clear. 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 Vinson’s order made no mention of an actual investigation. He said Verizon must turn over “all call detail records,” including “local calls … wholly within the United States.” On Capitol Hill, senators who serve on the Intelligence Committee said this is “nothing new” and has gone on since at least 2006.

Justice Department lawyers have not explained in public their interpretation of the law. Some outside experts say they must take the view that having access to the entire database of phone calls is “relevant” to investigating terrorism plots.

“This is all about searching for patterns of calls,” said Washington attorney Stewart Baker, a former general counsel for the National Security Agency. He said he had no actual knowledge of the current program, but he said having access to the phone records would allow the NSA to link calls to suspected terrorists, here or abroad.

Q: How has this broad surveillance program remained secret?

A: Because lawmakers in the Senate and House voted to keep it secret from the public. 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 phone records in this country. The president and the Supreme Court have helped maintain the secrecy. Barack Obama’s Justice Department has refused to release its legal explanations of the law. For its part, the high court has tossed out lawsuits from civil libertarians on the grounds that none of them could prove they were secretly wiretapped.