“Anything that yesterday’s disclosures add to the ongoing public debate,” it continued, “is outweighed by the road map they give to our adversaries about the specific techniques we are using to try to intercept their communications in our attempts to keep America and our allies safe and to provide our leaders with the information they need to make difficult and critical national security decisions.”

But if intelligence officials felt a sense of betrayal by the disclosures, Internet security experts felt a similar letdown — at the N.S.A. actions.

“There’s widespread disappointment,” said Dan Kaminsky, a prominent security researcher. “This has been the stuff of wild-eyed accusations for years. A lot of people are heartbroken to find out it’s not just wild-eyed accusations.”

Sascha Meinrath, the director of the Open Technology Institute, a research group in Washington, said the reports were “a startling indication that the U.S. has been a remarkably irresponsible steward of the Internet,” which he said the N.S.A. was trying to turn into “a massive platform for detailed, intrusive and unrestrained surveillance.”

Companies like Google and Facebook have been moving to new systems that, in principle, would make government eavesdropping more difficult. Google is in the process of encrypting all data that travels via fiber-optic lines between its data centers. The company speeded up the process in June after the initial N.S.A. disclosures, according to two people who were briefed on Google’s plans but were not authorized to speak publicly about them. The acceleration of the process was first reported Friday by The Washington Post.

For services like Gmail, once data reaches a user’s computer it has been encrypted. But as messages and other data like search queries travel internally among Google’s data centers they are not encrypted, largely because it is technically complicated and expensive to do.

Facebook announced last month that it would also transition to a novel encryption method, called perfect forward secrecy, that makes eavesdropping far more difficult.