The level of security on the Diebold machines is shameful. There are thousands of keys to the machine in circulation (the security is slightly better than a suitcase lock, but not by much). Someone with a key to a machine and a suitably-formatted memory card can do whatever they want with the software in the machine. Their software can if desired alter votes and then erase any trace of itself.
Any machine used for voting should have all code and parameters stored on a medium that can be read out in its entirety without running any code thereon, and can be protected against alteration from before the time it's read by both parties before the election until after the time it's read by both parties after the election. One of many simple and fundamental security principles that Diebold completely failed to grasp (that a mini-bar key can open the machines is just the icing on the cake).
The Ohio Diebold machines have paper trail stored in them.