Machines that use paper ballots scanned with optical scanning readers are more secure because voters have filled out the ballots themselves and a paper trail is available for any necessary recounts, he said. Although film documentaries are being made about the vote flipping problems -- and potential conspiracy theories -- "I'm not sure I buy that," Dill said. "But we definitely need to get to the bottom of it."

In his home precinct in San Mateo County, Calif., Dill said he voted on an optical scanning machine that automatically "read" the paper ballot he filled out with a pen. He wanted to try one of the new Hart InterCivic eSlate electronic machines the county bought, but the only one in his polling place was in use, he said. The eSlates used by San Mateo County include a paper record of the voter's choices that is printed out, he said.

The machines chosen by his county are not his preference, however. "I have long advocated precinct-scan optical scanning machines" using ballots filled out by voters and then read by scanners.