The recent penetrations of state voter registration databases in Arizona and Illinois have, so far, been limited to data exfiltration. Much of the information contained in voter registration databases is public anyway, so the primary concern is whether voter intimidation on a large scale is possible because personal information such as addresses is now collected in one place.
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But a scenario in which improper access enables hackers to selectively manipulate voter registrations, such as by deleting 10% of the registration records associated with Democrats, is far more worrisome. Voter registration databases often do contain party affiliation, and it could be a simple matter to preferentially deprive members of a particular party of the ability to cast a ballot on Election Day. If the election is close (as many expect it to be), it would not take a large number of selective deletions to tilt the election.
How will we know if that happens? What could be done about it even if it were proven? And what nation-state has the motive, means, and opportunity to conduct such a hack, and on which side?
Voters will have to be extra-diligent this year about making sure their voter registrations are active, and be prepared to challenge assertions that they are not properly registered to vote.