Voting integrity advocates had argued Georgia's electronic voting machines are unreliable and vulnerable to hacking, but a federal judge says forcing the state to change its system to paper ballots before the midterm elections is too risky.

But Whitmire said some voters in Pickens County cast paper ballots because of a mistake in preparing a device that poll managers use to open electronic voting machines. He said Pickens County elections officials were sending new devices where they were needed. He said each polling location had plenty of paper ballots to use until the machines were activated.

Dan Wallach, a computer scientist who acts as an adviser on national guidelines for voting machines, says: "With the newer machines that generate paper ballots - including the ones used in Georgia - any sort of computerised ballot stuffing would necessarily involve misprinting those paper ballots, which would be certain to be discovered while the election was ongoing."

An MDC official said the party had notified police it would demonstrate next Wednesday to press its demands. Thousands of MDC supporters marched to the ZEC offices on June 5, demanding reforms that the party said were vital for a credible vote.