I wonder what the odds are that the voting machines are hacked vs. abuse of absentee ballots? It seems to me that any solution that requires a person to physically appear at scattered polling places and tamper with hundreds of machines in a single day is probably not a huge problem.

If you can mass mail fake ballots to the registrar then that could be more of a problem. I would presume that most absentee ballot systems have some sort of check that they're not receiving a ballot back from someone who did not request one, but I also know that this sort of thing could fall through the cracks if there aren't proper safeguards in place.