The hole is considered more worrisome than most security problems discovered on modern voting machines, such as weak encryption, easily pickable locks and use of the same, weak password nationwide.
Armed with a little basic knowledge of Diebold voting systems and a standard component available at any computer store, someone with a minute or two of access to a Diebold touch screen could load virtually any software into the machine and disable it, redistribute votes or alter its performance in myriad ways.
"This one is worse than any of the others I've seen. It's more fundamental," said Douglas Jones, a University of Iowa computer scientist and veteran voting-system examiner for the state of Iowa.
"In the other ones, we've been arguing about the security of the locks on the front door," Jones said. "Now we find that there's no back door. This is the kind of thing where if the states don't get out in front of the hackers, there's a real threat."
This newspaper is withholding some details of the vulnerability at the request of several elections officials and scientists, partly because exploiting it is so simple and the tools for doing so are widely available.
A Finnish computer expert working with Black Box Voting, a nonprofit organization critical of electronic voting, found the security hole in March after Emery County, Utah, was forced by state officials to accept Diebold touch screens, and a local elections official let the expert examine the machines.
Black Box Voting was to issue two reports today on the security hole, one of limited distribution that explains the vulnerability fully and one for public release that withholds key technical details.
The computer expert, Harri Hursti, quietly sent word of the vulnerability in March to several computer scientists who advise various states on voting systems. At least two of those scientists verified some or all of Hursti's findings. Several notified their states and requested meetings with Diebold to understand the problem.
The National Association of State Elections Directors, the nongovernmental group that issues national-level approvals for voting systems, learned of the vulnerability Tuesday and was weighing its response. States are scheduled to hold primaries in May, June and July.
"Our voting systems board is looking at this issue," said NASED Chairman Kevin Kennedy, a Wisconsin elections official. "The states are talking among themselves and looking at plans to mitigate this."
California, Pennsylvania and Iowa are issuing emergency notices to local elections officials, generally telling them to "sequester" their Diebold touch screens and reprogram them with "trusted" software issued by the state capital. Then elections officials are to keep the machines sealed with tamper-resistant tape until Election Day.
In California, three counties San Joaquin, Butte and Kern plan to rely exclusively on Diebold touch screens in their polling places for the June primary.
Nine other counties, including Alameda, Los Angeles and San Diego, will use Diebold touch screens for early voting or for limited, handicapped-accessible voting in their polling places.
California elections officials told those counties Friday that the risk from the vulnerability was "low" and that any vote tampering would be revealed to voters on the paper read-out that prints when they cast their ballots, as well as to elections officials when they recount those printouts for 1 percent of their precincts after the election.
"I think the likelihood of this happening is low," said assistant Secretary of State for elections Susan Lapsley. "It assumes access and control for a lengthy period of time."
But scientists say that is not necessarily true.
Preparations could be made days or weeks beforehand, and the loading of the software could take only a minute or so once the machines are delivered to the polling places. In some cases, machines are delivered several days before an election to schools, churches, homes and other common polling places.
Scientists said Diebold appeared to have opened the hole by making it as easy as possible to upgrade the software inside its machines. The result, said Iowa's Jones, is a violation of federal voting system rules.
"All of us who have heard the technical details of this are really shocked. It defies reason that anyone who works with security would tolerate this design," he said.
Contact Ian Hoffman at email@example.com.