The website for the National Security Agency (NSA) was online Saturday morning following rumors that hackers had brought the system down the previous day.
NSA.gov appeared fully functional after going offline Friday at about 2 p.m. for several hours.
The dysfunction prompted hactivist group Anonymous to claim the site had been the target of a denial-of-service attack, when a site collapses under a flood of traffic from hackers.
The agency denied that the site's problems were the product of an attack, attributing the issues instead to "an internal error that occurred during a scheduled update."
The back-and-forth comes as the Obama administration faces strong criticism from allies over the NSA's brood snooping activities, which allegedly include tapping the phone lines of foreign leaders.
Techies concerned about surveillance are planning a march in Washington, D.C. Saturday morning to demonstrate their opposition to the practice.