By Barbara Starr

U.S. intelligence now believes Edward Snowden did not gain access to the "crown jewels" of National Security Agency programs that secretly intercept and monitor conversations around the world, CNN has learned.

The Obama administration is reviewing what the admitted leaker of classified information actually got his hands on and what damage he may have caused.

The ongoing damage assessment indicates he did not gain access to what is called ECI or "extremely compartmentalized information," according to a U.S. official familiar with the review.

Snowden fled to Moscow after his leaks in June and has been stranded at the Moscow airport awaiting a response to his request for temporary asylum. He faces espionage charges in the United States.



With Snowden still at large and the publication of agency surveillance secrets publicized, the intelligence community may have good reason to downplay the impact of what he has revealed.

However, the official said the intelligence community remains adamant that Snowden caused serious damage. The administration believes it knows the extent of the material that was downloaded.

"We are not downplaying it," the official said, explaining that assessing the matter over weeks has enabled authorities to focus more directly on the impact of Snowden's actions.

The official spoke to CNN on background because the assessment is not fully completed.

CNN cannot independently verify the statements made either by the administration or Snowden.

Officials do not dispute that Snowden had critical information about how NSA programs worked.

"But just because you have the blueprints doesn't mean you have the manual," the official said.

A key question is whether Snowden, a former NSA contractor, really knows how the programs work at a detailed technical level.

Snowden did leak sensitive documents about anti-terror programs, detailing secret telephone metadata and e-mail surveillance.

U.S. officials have said that terror groups are aware of the Snowden leaks and are responding internally, like adjusting communications and security.

NSA Director Keith Alexander said last week the United States has concrete proof terrorists are making changes and taking actions that are going to "make our job harder."

Other officials are less resolute about the extent of the exposure.

The top lawyer for the Office of the Director of National Intelligence said it is not clear how much U.S. adversaries will adjust based on what is known already.

"It's too early to tell yet whether it is going to have an impact, but there's no question that they have sat up and taken notice of specifically what has been released here and the impact it has on their communications," Robert Litt, general counsel for the national intelligence office said last Friday.

The assessment also has concluded that Snowden took advantage of knowing that a good deal of information was concentrated in one portion of the NSA's computer system.

"What he had was information that was centralized so it could be shared broadly," the official said.

This is similar to the assessment reached in the case of Army Pvt. Bradley Manning where information was stored in ways that large numbers of personnel could access it under certain circumstances.

Manning is accused of leaking documents to WikiLeaks in the largest case of its kind in U.S. history. He is currently on trial before a military court.

Deputy Defense Secretary Ashton Carter said last week that Snowden exploited a weakness that came from a desire to make the information more accessible to those in the intelligence community.

"In an effort for those in the intelligence community to be able to share information with one another, there was an enormous amount of information concentrated in one place," Carter said during a panel at the Aspen Security Forum. "It creates too much information in one place."

As such, the government has accelerated efforts to better secure classified information, improvements that had begun even before Snowden went public.

The government believes Snowden was aware that upgrades were being made to NSA systems tagging data and users so that downloads were recorded, but Snowden accessed portions where that work had not been completed.

In addition, system administrators like Snowden and others will be subject to more stringent rules.

Downloads will require a second more senior employee to "watch, log and observe" what material is being accessed the official said. Access codes and passwords also have been changed.