The initial test was to be held last week but was postponed, said Jim March, an investigator at Black Box Voting Inc., a Renton, Wash.-based nonprofit voter advocacy group.

Plans for the California test come amid recurring concerns that e-voting gear, including optical scan and touch-screen voting machines, are vulnerable to intrusion or rigging.

March's organization prodded California Secretary of State Bruce McPherson's office to test Diebold's AccuVote optical scan equipment for possible vulnerabilities after a check of the machines in Florida revealed problems.

March said the Leon County, Fla., test in May determined that a vulnerability in the memory card in the Diebold optical scan machine could allow a hacker to replace code and "doctor the results."

The California test is expected to be carried out by Finland-based security expert Harri Hursti, who conducted the Florida test in conjunction with Black Box. It hasn't been determined whether Black Box will be involved in the California trial run.