By Richard Black
BBC Science correspondent, in Seattle
Two leading American experts on computer voting have warned that the forthcoming US presidential election could be more chaotic than the last.
The 2000 presidential election descended into farce
They told a Seattle conference that the new systems may be less reliable than those used four years ago.
The issue of voting systems came to the fore during the controversy over ballot papers in the crucial state of Florida.
The question of what really counts as a vote - a clear hole in a ballot paper, or a bulge? - was hotly debated.
About 25% of the US electorate is expected to vote electronically in this year's November presidential election. This is up from around 15% in 2000.
Following the fiasco in Florida, the Bush administration passed a bill called the Help America Vote Act, aimed in part at persuading states to switch to electronic voting.
But Professor David Dill from Stanford University told the annual meeting of the American Association for the Advancement of Science the switch may actually make things worse.
"The problem with electronic voting is your votes disappear into the electronic machine and there is no independent way to check that those results are valid," said Professor Dill.
"I know that I am not going to have a lot of confidence in the vote totals reported by those machines unless there is some independent polling or whatever that is consistent with that."
In recent years there has been a spate of disputes over local election results across the US involving voting machines.
There are many different models, and some provide the voter with no record of how he or she has voted - no evidence that the machine recorded the vote correctly.
The Brazil example
Professor Ted Selker, from the Massachusetts Institute of Technology, told the meeting that the machines were not sufficiently secure.
He said there could and should be safeguards to prevent anyone tampering with their computer code before and after voting.
Data should be extracted from the machines after voting by someone other than the company which made them, he continued.
Other countries, notably Brazil, he said, had introduced e-voting with appropriate safeguards and had shown that it could work well.
"In the early 90s, they set up a system whereby three different organisations worked together - but they were separate.
"One came up with the requirements, one to make a reference software platform and finally the election commission to evaluate those. And through several elections they came up with better and better voting machines, which regained confidence in the government.
"I believe in our country we should have experts that are separate from the voting companies who are available to improve the equipment and the process of testing them."