I write software for scanner systems. Modifying the software to ignore some votes, or to slip them into another column is trivial, and oh by the way, the software for them is on ROM chips in sockets or even better, on removable memory.
Modern voting machines are no less secure than any system that we've had in the past--it's all HYPE to instill doubt in our electoral system.
If I believed in conspiracies, I'd believe that the hype is to make it easier to install a "benevolent" socialist dictator, or to further the idea that only the "ruling class" were qualified and honest enough to vote. But that's not me. I believe that all the hype is because global warming is allowing more x-rays to penetrate the atmosphere and is frying the brains of Princeton Professors.
Actually, the electronic systems are less reliable and less secure than paper ballots, as determined by computer scientists who were expecting to confirm the converse. This is reported in a "National Geographic" article on the subject:
http://news.nationalgeographic.com/news/2004/11/1101_041101_election_voting.html