Election officials in Chicago say the personal information of 1.8 million voters was found unsecured on the Internet.
The file was found by cybersecurity firm UpGuard.
It was the responsibility of Election Systems & Software, a vendor that provides Chicago with electronic lists of voters for use in polling places.
Left exposed were names, addresses, birthdates and parts of Social Security numbers.
Chicago Board of Election Commissioners spokesman Jim Allen says he has no reason to believe the information was obtained by criminals. That said, “every one of these little events has the possibility to erode people’s confidence in the election system.”
The vendor, which also supplies voting machines to dozens of states, says it shut down the server within hours of learning of the problem.
Chicago officials say the data did not include voting history or relate to election results.