U.S. officials said that the Iranian hackers behind a wave of threatening emails sent to thousands of Americans earlier successfully accessed voter data.

The statement, issued jointly by the FBI and the Department of Homeland Security’s Cybersecurity and Infrastructure Security Agency (CISA), partially confirms the authenticity of a video distributed as part of a disinformation campaign.

The campaign featured a video in which a hacker purported to demonstrate how they could cause havoc by breaking into a voter registration records.