Re: Hacking or Deliberate
Many, if not most, US electronic voting machines do have a paper trail in the form of a printed paper tape. During the final part of the voter interaction the tape was printed and displayed under a locked transparent panel as the voter's choices were shown on the screen. A diligent voter would have no trouble verifying that (a) the selections shown on the screen were those he or she made during the vote collection phase, and (b) were the same as those shone on the paper tape.
That was true of the Diebold machines in Ohio that I used and, as an election official, managed during the period from about 2002 to 2005, and also of the identical appearing machine with a different label that I used last election in Utah.
That said, it probably is true that corrupt software in the machines could show one thing on the screen, the same thing on the tape, and something a bit different on the memory card used for the data collection. To make that stick, it also would be necessary for the same corrupt software to show identical sums on the screen, the end of the tape, and internal to the memory card, but the same corrupt software should have no trouble with that.
Probably the best compromise overall is the manually prepared optically scanned ballot, which gives decently rapid results, is easy for the voter, and also easy to recount if there is a question. I understand Ohio transitioned to that as the earlier machines got to EOL, and I was a bit surprised to see the older variety in Utah.