CHICAGO (CBS) — Chicago election officials say they are investigating a security breach involving data from city voters and a contractor for the election board.

Chicago Election Board spokesman Jim Allen said a well-known security expert who scours the Internet found names and other data from nearly two million Chicago voters and called the authorities. WBBM’s Political Editor Craig Dellimore reports.

“As far as we know now, Chris Vickery the Internet researcher, cybersecurity researcher is the only person with this file. We were most concerned that it was out there at all,” he said.

Allen said the data turned out to be backup files stored on an outside server for Election Systems & Software, the vendor that manages the polling books. Somehow private settings switched to public.

“It’s not a server that we manage or control in any way, shape or form. And until this happened, we had no idea that it even existed,” he said.

Jim Allen said the server was shut down just hours later. An investigation is underway.

Elections officials say no registrations or elections were affected.