Secret to Prism program: It's just one part of an even bigger data seizure
But Internet data doesn't care about borders. Send an email from Pakistan to Afghanistan and it might pass through a mail server in the United States, the same computer that handles messages to and from Americans. The NSA is prohibited from spying on Americans or anyone inside the United States. That's the FBI's job and it requires a warrant.
Despite that prohibition, shortly after the Sept. 11 terrorist attacks, President George W. Bush secretly authorized the NSA to plug into the fiber optic cables that enter and leave the United States, knowing it would give the government unprecedented, warrantless access to Americans' private conversations.
Tapping into those cables allows the NSA access to monitor emails, telephone calls, video chats, websites, bank transactions and more. It takes powerful computers to decrypt, store and analyze all this information, but the information is all there, zipping by at the speed of light.
"You have to assume everything is being collected," said Bruce Schneier, who has been studying and writing about cryptography and computer security for two decades.
The New York Times disclosed the existence of this effort in 2005. In 2006, former AT&T technician Mark Klein revealed that the company had allowed the NSA to install a computer at its San Francisco switching center, a spot where fiber optic cables enter the U.S.
What followed was the most significant debate over domestic surveillance since the 1975 Church Committee, a special Senate committee led by Sen. Frank Church, D-Idaho, reined in the CIA and FBI for spying on Americans.
Unlike the recent debate over Prism, however, there were no visual aids, no easy-to-follow charts explaining that the government was sweeping up millions of emails and listening to phone calls of people accused of no wrongdoing.
The Bush administration called it the "Terrorist Surveillance Program" and said it was keeping the United States safe.
"This program has produced intelligence for us that has been very valuable in the global war on terror, both in terms of saving lives and breaking up plots directed at the United States," Vice President Dick Cheney said at the time.
The government has said it minimizes all conversations and emails involving Americans. Exactly what that means remains classified. But former U.S. officials familiar with the process say it allows the government to keep the information as long as it is labeled as belonging to an American and stored in a special, restricted part of a computer.
That means Americans' personal emails can live in government computers, but analysts can't access, read or listen to them unless the emails become relevant to a national security investigation.
The government doesn't automatically delete the data, officials said, because an email or phone conversation that seems innocuous today might be significant a year from now.
What's unclear to the public is how long the government keeps the data. That is significant because the U.S. someday will have a new enemy. Two decades from now, the government could have a trove of American emails and phone records it can tap to investigative whatever Congress declares a threat to national security.
The Bush administration shut down its warrantless wiretapping program in 2007 but endorsed a new law, the Protect America Act, which allowed the wiretapping to continue with changes: The NSA generally would have to explain its techniques and targets to a secret court in Washington, but individual warrants would not be required.
Congress approved it, with Sen. Barack Obama, D-Ill., in the midst of a campaign for president, voting against it.
"This administration also puts forward a false choice between the liberties we cherish and the security we provide," Obama said in a speech two days before that vote. "I will provide our intelligence and law enforcement agencies with the tools they need to track and take out the terrorists without undermining our Constitution and our freedom."
When the Protect America Act made warrantless wiretapping legal, lawyers and executives at major technology companies knew what was about to happen.
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