The National Republican Congressional Committee says it suffered a major hack earlier this year.
A spokesperson for the NRCC told several media outlets it was hit by a "cyber intrusion by an unknown entity." The committee said it was made aware of the attack in April and immediately launched an internal investigation into the matter. The FBI is also reportedly looking into the breach.
Anonymous sources told Politico thousands of sensitive emails from the accounts of four senior NRCC aides were exposed in the hack. The content of those emails is unclear, but sources say donor information wasn't exposed.
According to Politico, officials decided not to make the attack public because they didn't want to compromise their search for the culprit. The NRCC says it won't comment any further on the incident in order to protect the integrity of its investigation.