MELISSA BLOCK, HOST:

That lawsuit over NSA surveillance would likely never have happened if former NSA contractor Edward Snowden hadn't leaked classified documents that showed what the agency was doing. Snowden also revealed that the U.S. government was monitoring the communications of foreign leaders, among other secret activities. Intelligence officials say they're still coping with the ramifications of all these unauthorized disclosures.

NPR's Tom Gjelten has been covering the Snowden leaks since they became known in June, and he joins me now.

And, Tom, you've been learning more about just how Edward Snowden was able to get access to all these classified documents, given that he had a relatively low-level position as an NSA contractor.

TOM GJELTEN, BYLINE: Right, Melissa. First of all, he was a systems administrator. And anyone who's dealt with an IT helpdesk knows the systems administrator in a network can basically get into any computer in that network.

Now, in this case, Snowden had even more access than a normal systems administrator would have, because the NSA was running a software program called SharePoint that's for file sharing. The idea was that analysts working on a task could see all the documents that might be relevant to that task. Edward Snowden, working in Hawaii, was actually administering that SharePoint program. He actually had the job of working with those documents, moving them around, downloading them if necessary. That's how he had access. Not surprisingly, the NSA is not using that program anymore.

BLOCK: Tom, is it clear just how many documents Edward Snowden took?

GJELTEN: I think what's most clear, Melissa, is how many he could theoretically have taken based on the access that he had. And that figure - and the NSA is not disputing it - the last figure that we've heard is 1.7 million documents. But the NSA is not actually sure that he took all those documents with him when he left, and Snowden hasn't said.

So the NSA director, Keith Alexander, has said that Snowden had shared up to 200,000 documents with the reporters that he's worked with. What we don't know is whether there are even more documents beyond these that he has already shared.

BLOCK: I have to confess, Tom, that I have lost track of just what those documents have revealed. I felt like in the beginning, in June, when this was coming out, I had a pretty good handle on it. But every time I open the newspaper, it feels there's some new revelation. Can you try to bring us up to speed?

GJELTEN: Melissa, I've been covering this and I sometimes have the same problem. There are, as I understand it, four broad categories of documents that he has taken. And the first category includes all these documents that reveal the NSA's surveillance capabilities. And to sum that up, there are two big programs that have come out. The first one was the collection of telephone records. The second one involved the collection of Internet communications records.

Now, the phone program was by far the most important because the NSA, we learned, is collecting data about all the phone calls that Americans make. They don't have to be a target - all the phone calls, the records of those phone calls.

BLOCK: The metadata as it's called.

GJELTEN: The - they call it the metadata. And the second big program was about Internet records. Those are only Internet records that involve an overseas component. But in both cases, the NSA can initially sort of search that data without permission. Then, if they find something that is suspicious and it involves a U.S. person, then they have to go to a court order. So that's the sort of the sequence of programs that we've learned about.

BLOCK: OK. So that was the first category. But you said there are four. So what are the other three categories?

GJELTEN: The second category are the documents that include the actual intelligence reports that NSA analysts write about what's going on in the world, what they're overhearing, the threats, et cetera, the actual text reports. The third category are documents that talk about the NSA's partnerships with other intelligence agencies, obviously a very sensitive one as well.

The fourth category - and this is the most critical one - is basically all the documents that have the assignments, the to-do lists that the NSA gets from other departments in the government. What are the questions that the government wants the NSA to answer?

The NSA thinks that there may be 30,000 or more documents in that fourth category. Those are the ones they're most worried about. But this is important, Melissa: as far as we know, none of those documents has come out yet.

BLOCK: Tom, behind all this, there is an ongoing feisty, fierce debate about whether U.S. national security has actually been damaged as a result of Edward Snowden's disclosures.

GJELTEN: All right, Melissa. In a real narrow sense, let's say U.S. counterterrorism capabilities, there's no evidence yet that it really has suffered serious damage. In a broader sense, the U.S. standing in the world has been clearly damaged as a result of these disclosures of what the NSA is doing. The world didn't know the NSA was snooping to this extent. That has really hurt the U.S. reputation. Finally, of course, U.S. commercial interests have been damaged. U.S. tech companies, their fortunes have really taken a hit as a result of these disclosures.

BLOCK: OK. NPR's Tom Gjelten. Tom, thanks.

GJELTEN: You bet. Transcript provided by NPR, Copyright NPR.