U.S. government networks were hit by a cyberattack affecting several federal agencies, Cybersecurity and Infrastructure Security Agency Director Jen Easterly confirmed Thursday.

The attack does not pose a major risk to national security, Easterly said.

CISA, a part of the Department of Homeland Security, previously identified a gap in software security believed to have been exploited in attack.

A spokesperson for Mandiant, the cyber intelligence arm of Google Cloud, said government data was stolen in the attack.

This is a developing story. Please check back for updates.