Chicago voter data including names, addresses, birthdates, and other information was published publicly online briefly before being secured, election officials say.
The Chicago Board of Election Commissioners revealed Thursday the information for the city's 1.8 million registered voters uploaded to Amazon Web Services was publicly accessible for an unknown period, The Associated Press reported.
The Chicago Tribune reports the files had been uploaded by Election Systems & Software, a contractor that helps maintain Chicago's electronic poll books. A data security researcher alerted officials to the existence of the unsecured files on Saturday.
Election Systems reported in a statement it had "promptly secured" the files Saturday evening and has launched "a full investigation."
Elections board spokesman Jim Allen says the board is considering how to notify and potentially offer remedies to those whose information was exposed.