The report by researchers at the influential National Institute of Standards and Technology said the paperless voting machines — essentially notebook computers programmed to display ballot images and record voter choices — "in practical terms cannot be made secure."
"Many people, especially in the computer engineering and security community, assert that the (voting machines) are vulnerable to undetectable errors as well as malicious software attacks," the report said.
A key weakness is that there is no audit mechanism or paper trail to verify election results other than what the machine itself reports, the report said.
"Potentially, a single programmer could 'rig' a major election," the report said.
After examining the issue, including volunteering as election workers at polling sites, NIST researchers said in their report that they concluded that they not know how to write "testable requirements" to make the machines secure and it is their recommendation that the machines "in practical terms cannot be made secure."
Many states bought the paperless electronic voting machines with money provided by Congress after the 2000 presidential election, whose disputed results went all the way to the Supreme Court.
Gail Porter, NIST's public affairs director, emphasized that the draft report is a "discussion document" whose conclusions and recommendations could change.
The report will be discussed at a meeting Monday by NIST's Technical Guidelines Development Committee at the agency's headquarters in Gaithersburg, Md. The committee is tasked under a law enacted by Congress in 2002 to advise the Election Assistance Commission on developing guidelines for voting systems.
Election experts applauded the report's findings.
"The new NIST report is confirmation that the mandatory verified voter trails the DNC and its Voting Rights Institute have championed are vital to restoring the confidence of the American people in their own democracy," Donna Brazile, chair of the Democratic National Committee's Voting Rights Institute, said in a statement Friday.