Jack Balkin explains the fraud potential of electronic voting machines, and proposes a legal strategy to fight the problem based on Bush v. Gore. The technical solution seems fairly obvious: the machines should produce printed ballots that get physically deposited in a ballot box at the polling place. That makes the electronic count done by the machine auditable.
Glenn Reynolds has proposed a simpler solution: going back to paper ballots. But though paper does create the ability to recount, it’s subject to lots of other tricks. (The old mechanical lever voting machines I grew up with were actually fairly fraud-resistant, but no one’s making them any more.) That’s a serious problem, given the increasing use of absentee voting, which so far is entirely paper-based. Electronic absentee voting would be really hard to manage. [Here are some expert thoughts on that from Rebacca Mercuri.] The only fix I can think of is to have each voting transaction handled simultaneously by three counting systems, which would mean that an implausible level of collaboration would be required to make cheating effective.
That we have a real problem isn’t in much doubt; the case in Como County, Texas in which three Republican candidates had exactly the same number of votes county-wide but different numbers on a precinct-by-precinct basis is far more consistent with poorly-executed cheating than it is with coincidence.