The NSA.gov site was the target of a distributed denial of service (DDoS) attack afternoon.
Twitter accounts belonging to the Anonymous hacktivism movement have suggested they are responsible.
“Aww don’t panic about nsa.gov being down. They have a backup copy of the internet,” according to a tweet from the handle @AnonyOps.
A DDoS attack overwhelms a website’s servers with Internet traffic in an attempt to crash the site. DDoS attacks are illegal in the US under the Computer Fraud and Abuse Act.
A spokesperson for the NSA said they are “looking into the issue,” adding the agency’s internal network was “not at all” compromised.
The NSA’s spying activities sparked outrage over the summer following revelations about the agency’s global surveillance programs from former NSA contractor Edward Snowden.
The agency has been criticized for its electronic eavesdropping on millions of Americans as well as citizens and even leaders of foreign countries.