Two years ago, hackers gained access to an online voting system created by the District of Columbia and altered every ballot on behalf of their own preferred candidates. On the “Thank You!” page that ran at the end of the voting protocol, they left their trademark—the University of Michigan fight song. The online voting system was real, intended for use that November, but the compromised election, fortunately, was just a mock-up for testing security. The infiltrators were a team of graduate students led by University of Michigan computer scientist J. Alex Halderman. Which candidates got the fake votes? Skynet from the “Terminator” movies and Bender, the alcohol-fueled robot from TV’s “Futurama.” But the hackers had a serious point: that Internet voting systems were a real threat to the integrity of the democratic process. “The question of whether Internet voting is secure is really not a political question,” Dr. Halderman says. “It’s a technical question.” As many as three million voters will be eligible to vote online this fall, according to Pamela Smith, executive director of the Verified Voting Foundation, a nonpartisan fair elections watchdog group. In all, 31 states will offer some form of online voting, usually for overseas voters.