Gen. Michael Hayden, a former director of the National Security Agency, tells NPR's Weekend Edition Sunday that the government's acquisition of phone records and surveillance of Internet activity is lawful and justified by the changing nature of the war on terrorism.

Hayden, who served as NSA chief from 1999-2005 and is also a former CIA director, says NSA's activities are "perfectly legal" and "an accurate reflection of balancing our security and our privacy."

The program of gathering phone record metadata, first detailed in The Guardian newspaper last week, is analogous to collecting the haystack in case you should suddenly need to find a needle, he tells NPR.

"We roll up an al-Qaida cell somewhere, let's just say Yemen," he says as an example. "We grab a cell phone. We know through the pocket litter that the owner of that cell phone is involved in terrorist activity. We didn't know about that cell phone before. We didn't have that number."

But only with the number can the agency run it through the metadata and parse correlations and connections. Otherwise, the information is put away and "not touched," he says.

"So fears or accusations that the NSA then data mines or trolls through these records, they're just simply not true," Hayden tells host Rachel Martin.

Before the NSA started collecting such data, the agency found itself at a dangerous disadvantage, he says. For example, prior to Sept. 11, 2001, the agency knew about Khalid al-Mihdhar and Nawaf al-Hazmi, the two individuals who piloted the jetliner that hit the Pentagon.

"NSA actually intercepted about half a dozen phone calls from those guys in San Diego calling a known al-Qaida safe house ... in the Middle East," Hayden says. "Nothing, nothing in the physics of the intercepts, or in the content of the communications, told us these guys were in San Diego. If we would have had this program in place ... we would have known these two known terrorists were living in San Diego," he says. "That's a big deal."

Hayden says the Foreign Intelligence Surveillance Act court gives NSA a "generalized approval" to search the metadata, given probable cause.

He says another program known as PRISM, which has been described in media reports as a top-secret data-mining program, is "about Internet data, not telephony, and it's all about foreigners."

"So, if I've got a bad person in Waziristan, talking to a bad person in Yemen, via a chat room that is hosted by an American Internet service provider, the only thing American about that conversation is the fact that it's happening on a server on the West Coast of the United States," he says.

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