The FBI said Friday it has notified Congress about a data breach it has labeled a "major incident," which reportedly targeted a bureau surveillance system.

The bureau did not specify who it believes is behind the data breach, but several outlets have reported that China-linked hackers are suspected of being behind the incident.

It was not immediately clear when the breach occurred, but it amounts to a "major incident" under the Federal Information Security Modernization Act. A "major incident" is described as “any incident that is likely to result in demonstrable harm to the national security interests, foreign relations, or economy of the United States,” according to The Hill.

“The FBI identified anomalous activity on an unclassified network and quickly leveraged all technical capabilities to remediate the incident,” the FBI said in a statement. “It was determined the access was obtained through a third party and constitutes a major incident under [FISMA].

“The FBI is following the required steps under FISMA, including notifying Congress, and remains focused on countering nation-state and cybercriminal activity,” the bureau added.

Misty Severi is a news reporter for Just The News. You can follow her on X for more coverage.