Election Systems & Software (ES&S), the Nebraska-based voting software and election management company, confirmed the leak on Thursday.
In a blog post, the company said the voter data leak contained names, addresses, birthdates, partial social security numbers and some driver's license and state ID numbers stored in backup files on a server. Authorities alerted ES&S to the leak on Aug. 12, and the data was secured.
A security researcher from UpGuard discovered the breach.
The data did not contain any voting information, like the results of how someone voted.
Jim Allen, a spokesman for the Chicago Board of Elections, said the leak did not contain or affect anyone's voting ballots, which are handled by a different vendor.