If ballot-marking devices are hacked or tampered with, they could print out falsified ballots, according to the study by professors with expertise in cybersecurity and statistics.

Many voters won't bother to double-check their paper ballots, and those that do might not notice inaccuracies, the study says. When a voter does find a problem, he or she could fill out a replacement ballot, but there’s no way to correct previous voters’ ballots affected by those problems.

“This is the essential security flaw of BMDs: Few voters will notice and promptly report discrepancies between what they saw on the screen and what is on the BMD print-out, and even when they do notice, there's nothing appropriate that can be done,” wrote the study’s authors, Princeton’s Andrew Appel, Georgia Tech’s Richard DeMillo and University of California, Berkeley’s Philip Stark.

In addition, the study warned that ballot-marking devices generally encode votes in bar codes alongside the printed text of voters' choices. Voters wouldn't be able to verify the accuracy of bar codes before they're scanned by tabulation computers.

Georgia Secretary of State Brad Raffensperger’s office didn’t provide comment when asked Tuesday whether ballot-marking devices are secure and accurate.