WASHINGTON, D.C. — The National Republican Congressional Committee was hacked in 2018 by an “unknown entity,” a committee spokesman acknowledged Tuesday.

“The NRCC can confirm that it was the victim of a cyber intrusion by an unknown entity,” spokesman Ian Prior said in a statement. “The cybersecurity of the committee’s data is paramount, and upon learning of the intrusion, the NRCC immediately launched an internal investigation and notified the FBI, which is now investigating the matter.”

Prior, who works for Mercury Public Affairs, said the NRCC will not be commenting further on the incident.

The FBI did not immediately respond to a request for comment.

The breach was first reported by Politico on Tuesday, citing committee officials who said hackers had access to email accounts of four “senior aides” and surveilled the accounts for several months.

The Democratic Congressional Campaign Committee was included in a hack of the Democratic National Committee in 2016, perpetrated by Russian hackers. That event led to internal emails and opposition research leaking to the public.

According to Politico, none of the NRCC emails accessed this year have been made public.