This Is Way Too Easy

The video shows how one can use a simple USB key to infect the laptop used to prepare the cards that initialize the various voting devices. As a result, the cards are loaded with a malicious software component.
When a card is inserted in a voting terminal, the malicious software exploits a vulnerability in the terminal loading procedure and installs a modified firmware, effectively "brainwashing" the terminal.
Later, when the terminal is used by the voters to cast their votes, the firmware uses a number of different techniques to modify the contents of the ballots being cast.
The movie also shows that the physical security measures being used to limit access to essential parts of the voting systems are ineffective.