Gen. Michael Hayden, Deputy Director of National Intelligence, spoke Monday at the National Press Club in Washington, D.C., and for those who follow the intelligence community closely, the speech was eye-opening. In addition to defending President George W. Bush’s “terrorist surveillance program,” Hayden confirmed and denied several details of NSA’s operations which had previously been a matter of wild speculation among such groups as conspiracy theorists.

“There’s a lot of information out there right now,” Hayden said. “Some of it is, frankly, inaccurate. Much of it is just simply misunderstood. I’m here to tell the American people what NSA has been doing and why. And perhaps more importantly, what NSA has not been doing.”

Hayden said he wanted to tell as much as possible, while still protecting critical intelligence sources and methods. As it turns out, he said quite a lot.

NSA intercepts communications, and it does so for only one purpose — to protect the lives, the liberties and the well-being of the citizens of the United States from those who would do us harm. By the late 1990s, that job was becoming increasingly more difficult. The explosion of modern communications in terms of volume, variety, velocity threatened to overwhelm us.

The agency took a lot of criticism in those days, I know, criticism that it was going deaf, that it was ossified in its thinking, that it had not and could not keep up with the changes in modern communications. And all of that was only reinforced when all of the computer systems at Fort Meade went dark for three days in January of 2000 and we couldn’t quickly or easily explain why.

Those were really interesting times. As we were being criticized for being incompetent and going deaf, at the same time others seemed to be claiming that we were omniscient and we were reading your e- mails. The Washington Post and New Yorker Magazine during that time — I’m talking 1999 now of 2000 — they wrote, incorrectly, that — and I’m quoting — “NSA has turned from eavesdropping on the communists to eavesdropping on businesses and private citizens.”

And that — and I’m quoting again — “NSA has the ability to extend its eavesdropping network without limits.” We are also referred to as a, quote, “global spying network that can eavesdrop on every single phone call, fax or e-mail anywhere on the planet.”

I used those quotes in a speech I gave at American University in February of 2000. The great urban legend out there then was something called “Echelon” and the false accusation that NSA was using its capabilities to advance American corporate interests — signals intelligence for General Motors, or something like that. You know, with these kinds of charges, the turf back then feels a bit familiar now. How could we prove a negative — that we weren’t doing certain things — without revealing the appropriate things we were doing that kept America safe? You see, NSA had, NSA has an existential problem. In order to protect American lives and liberties, it has to be two things: powerful in its capabilities, and secretive in its methods. And we exist in a political culture that distrusts two things most of all: power and secrecy. — Gen. Michael Hayden

Which explains all the conspiracy theories. You’re probably familiar with at least one of the many such wild theories out there about Echelon: that it’s a worldwide spy network used by the five countries in the UKUSA agreement to, among other things, spy on their own citizens. According to the theory, one of the five countries, the U.S., Canada, the U.K., Australia and New Zealand, can simply have the other four countries do the spying on their own citizens for them, so they can plausibly claim to not be spying on their own citizens.

It’s true that under the UKUSA Communications Intelligence Agreement of 1946, signed by these five countries, they share intelligence intercepts and share in the work breaking the cryptography. Using a computer network called PLATFORM (yes, they are very imaginative) which ties together several dozen computer systems of the five countries, and a software package called ECHELON which runs on the PLATFORM, each country can look through the intercepts collected by the other four, and submit targets it’s interested in to the other four, in case they happen to be collecting in those areas.

To date, no evidence has been brought forth that any of the UKUSA countries have used the PLATFORM set up in the agreement to collect signals intelligence on any of the other countries in the agreement, or in their own countries, outside of the law. The conspiracy theories remain just that, theories. And not very good ones, at that.

Anyway, back to Hayden and his discussion of the surveillance program. “[The program] is not a driftnet over Dearborn or Lackawanna or Freemont grabbing conversations that we then sort out by these alleged keyword searches or data-mining tools or other devices that so-called experts keep talking about,” he said.

I said this isn’t a drift net, all right? I said we’re not there sucking up comms and then using some of these magically alleged keyword searches — “Did he say ‘jihad’? Let’s get –” I mean, that is not — do you know how much time Americans spend on the phone in international calls alone, okay? In 2003, our citizenry was on the phone in international calls alone for 200 billion minutes, okay? I mean, beyond the ethical considerations involved here, there are some practical considerations about being a drift net. This is targeted, this is focused. This is about al Qaeda. — Ibid.

A billion minutes a day in international calls entering and leaving the country sounds about right. Which means a few hundred thousand calls in progress at any given moment. Even with NSA’s acres and acres of computers, processing that kind of volume of data in real time would require a lot more acres of computers. It’s one thing to switch and route the calls; the machinery needed to do that is very small by comparison to the machinery which would be needed to intercept, listen to the calls and pick out keywords.

It may be possible, but like you and me, NSA has limited resources, and has to decide what to do with them. If it devoted every computer it’s got to this sort of thing, it might be able to pull it off, but it likely couldn’t get anything else done. So the whole idea of every phone call being monitored is ridiculous and rather silly.

And back to the terrorist surveillance program, James Bamford himself actually showed up and asked a question about who makes the decisions on who to target under the program. Hayden responded that it is not a “shift supervisor” but senior NSA officials who make the decision. “They’re all senior executives, they are all counterterrorism and al Qaeda experts,” he said, “in military terms, a senior colonel or general officer equivalent; and in professional terms, the people who know more about this than anyone else.”

Bamford is the author of The Puzzle Palace and Body of Secrets, the two definitive unclassified works on the National Security Agency, and A Pretext for War, about the failure of U.S. intelligence in the 9/11 attacks and the war on Iraq.

Hayden said much more, and the speech and press Q and A is well worth reading.