The man behind the NSA data-mining stories

(CBS News) WASHINGTON - The National Security Agency's surveillance programs remained a secret for several years until this week, when a source leaked the information to columnist Glenn Greenwald at the British newspaper the Guardian. The director of national intelligence said the damage done by this leak is "irreversible." CBS News spoke with the writer about his article.

"I've been working on this story to varying degrees for probably about two months now," Greenwald said.

Greenwald has argued against too much government access to our personal records for years, first on his blog at and now at the Guardian.

Guardian columnist Glenn Greenwald broke the story about the U.S. government's surveillance programs concerning data mining.
CBS News

Greenwald's source leaked him a top-secret court order compelling Verizon to hand over phone records on an "ongoing, daily basis."

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Greenwald acknowledged the source is a reader of his. "Other than the fact that it's a person or persons who have intimate knowledge of the functioning of the National Security Agency and how the NSA operates, there's nothing else," he said. "It's an anonymous source who's confidential, and, of course, as a journalist, you understand that I wouldn't tell you anything about my source."

Intelligence analysts argue such leaks can have consequences.

When The New York Times revealed a secret program tracking terrorist financing back in 2006, officials believed terrorists changed the way they moved money.

Does Greenwald have any concerns that making these programs public will reduce the effectiveness of the programs or tip off terrorists?

"No," he said. "Terrorists already know because it's been discussed openly for many years that the government tries to eavesdrop on their conversation. Any terrorist who doesn't know that the government is going to try to eavesdrop on their conversation or read their email is not a terrorist who is ever going to be able to do anything effective."

Greenwald said the Obama administration tried to convince his editors at the Guardian not to expose some of the secrets because it might harm national security. He said his editors rejected that argument and decided to print the stories anyway.

Watch Nancy Cordes' extended interview with Glenn Greenwald here

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    Nancy Cordes is CBS News' congressional correspondent.