The National Security Agency says an internal system error caused its website to go down for several hours Friday during a scheduled update.

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.

The NSA said the problem would be resolved Friday night.

After the website went dark, a Twitter account affiliated with the hacker group Anonymous appeared to claim responsibility.

A tweet from the handle @AnonyOps read, “Aww don’t panic about nsa.gov being down. They have a backup copy of the internet.”

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There is no evidence that any information or data has been stolen from NSA’s network, and it is not clear what caused the outage, The Wall Street Journal reported.

The Journal reported another Twitter handle @annoymousAsia allegedly affiliated with Anonymous appeared to take credit for the attack tweeting, “We sail strong. #tangodown #nsa.”

Click for more from The Wall Street Journal.

The Associated Press contributed to this report.