This is why I have advocated that you have the opportunity to view your votes printed on a roll of paper through a window to verify that the votes are recorded correctly. If it is right, you finalizes the votes. If it is wrong, you go to the judge immediately (before the votes are added to the totals electronically) and both you and he open the window and X out and initial all the votes and you get a do-over.
Sounds as if a programmer could bypass that though. It could show you what you did, but then swap the vote on the way to electronically recording it.
At any stage of the process, it can be changed. If it shows it to you, so what? You say, yep that’s right, and it goes on to record the vote differently.
most people won't take the time to verify this, unless the votes arenn't tallieduntil after this is verified. the easiest way would be to have the voter fill out a paper form, then feed the form into a counting machine. the paper stays with the machine. touch screens are easy to manipulate, and just because the paper says you voted for candidate A doesn't mean that that who got the increment.