NSA website goes down - US official

"NSA.gov was not accessible for several hours tonight because of an internal error that occurred during a scheduled update. The issue will be resolved this evening," the spokesperson added. "Claims that the outage was caused by a distributed denial of service attack are not true."

The hacker group Anonymous joked about the website going down in a tweet without saying if it had played any role. "Aw don't panic about nsa.gov being down. They have a backup copy of the internet," it said.

Twitter users @AnonymousOwn3r and @TruthIzSexy both were quick to comment on the matter, and implied that a distributed denial-of-service attack, or DDoS, may have been waged as an act of protest against the NSA.

Allegations that those users participated in the DDoS — a method of over-loading a website with too much traffic — are currently unverified, and @AnonymousOwn3r has previously taken credit for downing websites in a similar fashion, although those claims have been largely contested.

Meanwhile an NSA spokesperson denied the website was under attack saying it was merely updating software:

"NSA.gov was not accessible for several hours tonight because of an internal error that occurred during a scheduled update. The issue will be resolved this evening. Claims that the outage was caused by a distributed denial of service attack are not true."

 The spy agency’s internal network was "not at all" bothered, nor was any classified information in danger, added the spokesperson.

The crippling of NSA.gov comes amid a series of damning national security documents that have been disclosed without authorization by former intelligence contractor Edward Snowden. The revelations in the leaked documents have impassioned people around the globe outraged by evidence of widespread surveillance operated by the NSA, and a massive "Stop Watching Us” rally is scheduled for Saturday in Washington, DC.

The loosely organized, international hacker collective has frequently clashed with US authorities over file-sharing as well as allowing banks to handle donations to the anti-secrecy group WikiLeaks.

The NSA has been at the center of a furor over its vast electronic surveillance operations, revealed in a series of leaks from former intelligence contractor Edward Snowden, who has obtained asylum in Russia.