Eight years on from the Florida chaos that introduced hanging chads to the world there have been reports of problems with touch-screen machines recording the wrong candidates in early voting.

These machines, which will be used by a third of American voters, have a simple interface that allows voters to cast ballots by pressing coloured areas on a screen.

Complaints first surfaced in West Virginia and have been repeated in Colorado, Tennessee and Texas. A number of voters in several Texas counties said that the machines flipped their votes from Democratic choices to Republican ones, and vice versa. In several instances officials were ordered to check the calibration of their machines.

Voting watchdog organisations wrote to 16 secretaries of state last week advising them of a problem with one make of electronic machine that caused votes for one candidate to be recorded as a vote for the rival.

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The problems followed a report last month from Princeton University’s Centre for Information Technology, which found that touch-screen machines could easily be manipulated. Andrew Appel, a professor, said the touch-screen machines used in 18 of New Jersey’s 21 counties could be hacked into in seven minutes. He added that someone could replace a machine’s memory chip with one containing a fraudulent computer program capable of changing the results.

The machines’ manufacturer, Sequoia Voting Systems, disputed the findings and New Jersey state election officials expressed complete confidence in the security of its machines.

In Florida electronic voting machines have been deemed too unreliable. They were used in a 2006 race for a congressional seat but in Sarasota County 18,000 votes were not recorded. Charlie Crist, the Governor, ordered that the entire state switch to voting machines called optical scan, which provide an old-fashioned paper trail. Voters use a pen or pencil to mark paper ballots, which are then fed into scanners that record the results.

Many believe that optical scanners – especially ones that count the ballots at the election precinct, not at a central office – are the most reliable method. Those error rate for those systems in 2004, according to a University of Missouri study, was 0.7 per cent. The study found that touch-screen machines had an error rate of 1 per cent.

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