The software that runs many high-tech voting machines contains serious flaws that would allow voters to cast extra votes and permit poll workers to alter ballots without being detected, computer security researchers said. We found some stunning, stunning flaws," said Aviel D. Rubin, technical director of the Information Security Institute at Johns Hopkins University, who led a team. Diebold Election Systems...has about 33,000 voting machines operating in the United States. The systems...could be tricked by anyone with $100 worth of computer equipment, said Adam Stubblefield, a co-author of the paper. "Practically anyone in the country -- from a teenager on up -- could produce these smart cards that could allow someone to vote as many times as they like." The list of flaws in the Diebold software is long, according to the paper, which is online at avirubin.com/vote.pdf. Ballots could be altered by anyone with access to a machine, so that a voter might think he is casting a ballot for one candidate while the vote is recorded for an opponent. Douglas W. Jones, an associate professor of computer science at the University of Iowa, said he was shocked to discover flaws cited in Mr. Rubin's paper that he had mentioned to the system's developers about five years ago. "That such flaws have not been corrected in half a decade is awful." Peter G. Neumann, an expert in computer security at SRI International, said the Diebold code was "just the tip of the iceberg" of problems with electronic voting.