With midterm elections less than two weeks away, some critics are raising doubts about the reliability of electronic voting machines, but the machines' manufacturers say they are sound.
"The equipment has been tested by independent agencies and federal agencies," said Mark Radke, the director of marketing for Diebold, the company that makes the machines.
Radke also told "Good Morning America" that the units that didn't have paper receipts had the same encrypted software as machines that printed out receipts.
Approximately 40 percent of Americans will use these machines to vote in November.
Casting a ballot with the touch of a screen is a new system that voters in at least 33 states will use on Election Day, but some critics are skeptical about the machines' reliability.
"We don't know what happens inside these machines. We as citizens are not allowed to know," said Edward Felten, a professor of computer science and public affairs at Princeton University.
Recently, Felten and his Princeton colleagues showed just how easy it was to tamper with the new technology.
They gave a voting machine a virus and flipped the outcome of a mock election.
Fifteen electronic voting states don't require paper receipts, which is the physical proof necessary for a recount.
Past elections using electronic voting machines show that glitches are possible.
In a recent Texas primary, some electronic ballots were counted six times.
In Maryland, voting machines froze midvote, causing Gov. Robert Ehrlich to publicly bash the expensive system.
"I don't care if we paid half a billion dollars or a billion dollars," Ehrlich said. "If it's going to put the election at risk, there's no price tag for a phony election."