The National Republican Congressional Committee (NRCC) was hacked during the 2018 midterm elections, according to a report from Politico. Republican officials said that hackers had access to four senior NRCC aides’ email accounts for “several months,” until a security firm discovered the intrusion in April. The NRCC launched an internal investigation and alerted the FBI, but it did not inform any Republican legislators until this week.

“The NRCC can confirm that it was the victim of a cyber intrusion by an unknown entity,” said Ian Prior of Mercury Public Affairs, a PR agency employed by the committee. “Upon learning of the intrusion, the NRCC immediately launched an internal investigation and notified the FBI, which is now investigating the matter.” According to Politico, party officials suspect that a foreign government was responsible for the hack, although they provided very little detail about it. The NRCC ostensibly kept the hack secret from congressional Republicans to avoid compromising the investigation.

This hack mirrors the hacking of Democratic National Committee networks during the 2016 presidential election, alongside other targets like Hillary Clinton’s campaign manager John Podesta. Russian state-sponsored hackers are believed to have carried out those attacks, and special counsel Robert Mueller indicted 12 people in connection with them this summer. But unlike those hacks, hackers haven’t released any of the data from the NRCC breach.