The D.C. Board of Elections announced Friday that in a data breach, hackers were able to access thousands of D.C. residents’ voter records.

In a release, DCBOE said it became aware a hacking group known as RansomVC got access to 600,000 lines of U.S. voter data on Thursday. DCBOE, alongside its “data security and federal government partners,” are now investigating the breach.

The board said it discovered a breach through its website and its hosting provider DataNet, and has since taken down its website as a precaution, which now displays a message saying “Website Under Maintenance.”

“DCBOE continues to assess the full extent of the breach, identify vulnerabilities, and take appropriate measures to secure voter data and systems,” a spokesperson wrote.

Although most voter registration data is public information, some can be made confidential by the board.