From The Open Voting Foundation:

“Diebold has made the testing and certification process practically irrelevant,” according to Dechert. “If you have access to these machines and you want to rig an election, anything is possible with the Diebold TS — and it could be done without leaving a trace. All you need is a screwdriver.” This model does not produce a voter verified paper trail so there is no way to check if the voter’s choices are accurately reflected in the tabulation.