By Andy Sullivan

WASHINGTON (Reuters) - Maryland's sleek new voting machines will be swathed in tamper-proof tape during Tuesday's primary election, but that won't make computer scientist Avi Rubin any more confident in the outcome.

State election officials decided to wrap their $55 million touch-screen systems in tamper tape and keep an eye out for suspicious behavior after a panel of experts said they were vulnerable to a variety of hacking techniques.

But Rubin, a Johns Hopkins University professor who has volunteered as an election judge, says the tape won't catch any software flaws that could affect the tallies.

"Wrapping them in tape just protects that malicious code physically," said Rubin, who discovered several flaws in election-system software last summer.

Hundreds of thousands of people in 10 states will vote on Super Tuesday, the biggest primary day yet in the Democratic presidential contest.

Voters in Maryland, Georgia and much of California will cast their ballots on e-voting systems, which have been widely adopted since Congress provided funds to upgrade the aging punch-card systems that figured prominently in the Florida recount battle in 2000.

In the November general election, 29 percent of the electorate is expected to use the ATM-like machines, according to Election Data Services Inc., a Washington consulting firm. "I know enough about computer systems to know there's no way to achieve that level of integrity with the current technology," said Stanford University computer science professor David Dill.

Election officials and independent groups like the League of Women Voters say the machines are easy to use, allow fewer voting errors and provide better access to the blind and other disabled voters than other methods.

"I'm confident, and I think that the citizens of Maryland can have a great deal of confidence" that the machines will record votes accurately on Tuesday, said Linda Lamone, Maryland's administrator of elections.

But a growing chorus of activists and computer experts say many of these systems are prone to the bugs, glitches and security holes familiar to any computer owner. Hackers could also secretly alter the outcome of an election, they say.

Democratic presidential candidates have criticized the head of one equipment maker, Diebold Inc., for his active role as a fund-raiser for President Bush's re-election campaign. Diebold CEO Walden O'Dell has since curtailed his political activities, a spokesman said.

One group, the California Voter Foundation, has urged voters to use absentee ballots rather than electronic systems.

Security concerns have prompted Ohio to delay certification of e-voting systems until at least the November election, a spokesman for Secretary of State J. Kenneth Blackwell said.

In California, a judge ruled on Feb. 18 that the state could use e-voting systems in its primary, even as the secretary of state considers whether Diebold should be banned for using uncertified software in last October's election.

"When machines have been tested for accuracy, they have been successful," said Doug Stone, a spokesman for California Secretary of State Kevin Shelley. "But we're talking about a lack of respect by this particular vendor for state law."

"We made some changes and regrettably, there was confusion on proper notification on those kinds of changes," said Diebold Election Systems spokesman David Bear.

"Voters should not have concern about vote tallies or the official outcome of any election," he said.

Diebold's e-voting systems contain an internal printer so election officials can double-check results, Bear said, and federal reviewers inspect the software before certifying it.

Advocates say voters would be more likely to trust e-voting systems if they could print out each vote for review after it was cast, as California will require by 2006.