The Security Mentor

Poll workers found that screens on new electronic poll books froze or shut down as they tried to record arriving voters.
"What's the problem? Machines break all the time. Just swap in a working machine and go", a hardheaded realist might say.

The problem is that reliable systems are easier to build than secure systems. If the vendors can't even get the machines to run, the chances that they'll resist tampering are nil. And in fact, one voter found

When she got to the section of the ballot listing candidates for the Democratic central committee, it was already filled out. Bradley said she had to remove the computer's choices and insert her own.

The other problem is that officials trusted the machines so much that they ran short on paper backups:

"They don't have a printed list" of eligible voters, "they don't have a backup," Wuethrich said. "So when the computer goes down, they can't even look at a list to see who's eligible to vote."