https://www.scientificamerican.com/article/the-vulnerabilities-of-our-voting-machines/

A few weeks ago computer scientist J. Alex Halderman rolled an electronic voting machine onto a Massachusetts Institute of Technology stage and demonstrated how simple it is to hack an election.

In a mock contest between George Washington and Benedict Arnold three volunteers each voted for Washington. But Halderman, whose research involves testing the security of election systems, had tampered with the ballot programming, infecting the machine’s memory card with malicious software. When he printed out the results, the receipt showed Arnold had won, 2 to 1. Without a paper trail of each vote, neither the voters nor a human auditor could check for discrepancies. In real elections, too, about 20 percent of voters nationally still cast electronic ballots only.