NSA: No Denial-of-Service Attack - ABC News The National Security Agency says its website nsa.gov was inaccessible for several hours during a scheduled update. The agency says an internal error in the system caused the problem. There had been speculation on the Internet that the online site had been hit with a denial-of-service attack, but the agency said that was not true. A denial-of-service attack is an attempt by outsiders to make a network unavailable to its intended users. The NSA said the problem would be resolved Friday night.