Security Breach and Spilled Secrets Have Shaken the N.S.A. to Its Core

A serial leak of the agency’s cyberweapons has damaged morale, slowed intelligence operations and resulted in hacking attacks on businesses and civilians worldwide.

WASHINGTON — Jake Williams awoke last April in an Orlando, Fla., hotel where he was leading a training session. Checking Twitter, the cybersecurity expert was dismayed to discover that he had been thrust into the middle of one of the worst security debacles ever to befall American intelligence.Mr. Williams had written on his company blog about the Shadow Brokers, a mysterious group that had somehow obtained many of the hacking tools the United States used to spy on other countries. Now the gr...