As the US heads into a historic and contentious presidential election, concerns over electronic voting technology could be about to stir up controversy over the legitimacy of some results.

Ironically, electronic voting machines were meant to make elections more reliable and secure. After the 2000 presidential election, when spoiled ballots and "hanging chads" sent the disputed result all the way to the Supreme Court, Congress began dispensing billions of dollars to help states replace punch-card ballots with more-sophisticated voting technology. Since then, however, concerns over the trustworthiness of electronic voting system have steadily grown.

Already in several key states, early voting has seen touch-screen voting machines "flip" votes from one candidate to another. Some voters casting early ballots in Virginia, Tennessee, and Texas say that machines have flipped their votes. All were able eventually to correct the mistake, but this has added a sense of urgency to long-held unease over the security and reliability of electronic voting systems.

Earlier this month, a report from Election Data Services (EDS), a Washington, DC-based firm that tracks election administration, said that electronic voting machine usage will drop this year for the first time ever. In Tuesday's election, 32.6 percent of all ballots will be cast using an electronic voting machine, compared to 37.6 percent in 2006, the equivalent of 10 million fewer voters. "Basically, the activists and the political scientists have kind-of won that battle," says EDS president Kimball Brace. "Most election administrators don't find it worthwhile trying to fight the battle and are trying to move on."

Nonetheless, that percentage will still be higher than it was during either of the last two presidential election races: in 2000, 22.0 percent of votes were cast electronically, compared to 29.2 percent in 2004. Also, several key swing states, including Ohio, Indiana, and Nevada, will rely heavily on electronic voting. Ohio and Indiana will use a combination of optically scanned paper ballots and electronic voting machines, while Nevada will rely almost entirely on electronic voting, according to the same EDS study.

Meanwhile, the political situation in Ohio couldn't be more tense. Republicans and Democrats are already wrangling in court about voter registration issues and so, if the race is particularly tight, the state could well be the scene of fierce legal action centered on electronic voting irregularities.

E-voting machines are receiving an unprecedented amount of attention from experts and activists. Grassroots organizations such as Black Box Voting and Video the Vote are urging voters to monitor the election and have already publicized problems with some voting machines, including touch-screen vote flipping.

Many computer security experts have previously raised concerns about the reliability and accountability of these machines, an issue that is complicated, they say, by the fact that they are manufactured by a number of different private companies and make use of proprietary (or undisclosed) computer code. In 2004, Avi Rubin of Johns Hopkins University, Dan Wallach of Rice University, and colleagues published an analysis of an electronic voting machine used in Maryland and concluded that the machine was "far below even the most minimal security standards applicable in other contexts."