By Cherri Gregg

PHILADELPHIA (CBS) — The Pennsylvania Supreme Court heard oral arguments today on the legality of electronic-record voting machines.

Voting rights advocates say they leave too much room for error.

“Computer data is, by design, alterable,” says Marian Schneider, an attorney on the team that represents two dozen plantiffs in a six-year-old challenge of direct record electronic (“DRE”) voting machines.

The machines record ballot selections electronically, but do not produce a paper record of each vote.

Plaintiffs say it’s impossible to verify an election using a DRE machine, which leaves the vote vulnerable to hackers.

The machines are currently used in Philadelphia and 53 other Pennsylvania counties.

“[The Secretary of the Commonweath] should use a system that has the verification method built in, which 17 counties in Pennsylvania already use,” Schneider says.

Steven Bizar, who represents the Commonwealth, says the state has run rigorous testing and thinks DREs work just fine.

“These machines have been used since 2006 — sixteen elections, three million votes — and there’s never been an instance of tampering,” he notes.    “The optical scanning machines that the [plaintiffs] favor are no different in terms of the quality of the security that they provide than the DRE machines.”

Bizar argued before the state Supreme Court that the Secretary of the Commonwealth has the discretion to use the machines that the state deems best, adding that no machines are tamperproof.

He says the secretary has put adequate safeguards in place.

“The voters in Pennsylvania should be assured that their votes are counted and are being counted appropriately,” he says.

The court is likely to rule in this issue before the end of the year.