Political campaigns use the voter registration lists to conduct phone canvassing, create mailing lists for brochures about candidates and to put together door-to-door efforts.

This is the second time since March that the issue of privacy has arisen in Ohio government agencies. Last month, an Ohio man sued the state for posting his and other residents' Social Security numbers for years on state Web sites where publicly searchable records are stored, showing retail purchases made using credit cards or bank loans.

According to Ohio officials, Social Security numbers have been used for years to help state elections officials confirm voter identities by cross-referencing the information with data from the state's Bureau of Motor Vehicles, according to BMV spokesman Fred Stratmann. The secretary of state's office would send the voter registration databases to the BMV, which then compared it to another registration database maintained by the American Association of Motor Vehicle Administrators (AAMVA) in Arlington, Va., Stratmann said. By cross-referencing the data, election officials confirmed the identities of voters, he said.

AAMVA is a tax-exempt, nonprofit organization that assists U.S. and Canadian governments with motor vehicle administration, police traffic services and highway safety.

Under the Help America Vote Act of 2002, voters must include only the last four digits of their Social Security numbers as part of their registrations to help confirm their identities, Stratmann said. That information is then cross-referenced against the AAMVA database, he said.