A missing computer backup tape containing personal information on state employees also holds the names and Social Security numbers of 225,000 taxpayers, Gov. Ted Strickland said.
The tape, stolen last week from a state intern's car, was previously revealed to hold the names and Social Security numbers of all 64,000 state employees, as well as personal data for tens of thousands of others, including Ohio's 84,000 welfare recipients.
The taxpayers' information was on the backup tape because they hadn't cashed state income tax refund checks.
Strickland said Wednesday an expert's review could reveal the tape contained more sensitive data.
The administration has maintained it does not believe the information has been accessed because it would require specific hardware, software and expertise.
But data security experts said the unencrypted tape, described by police as roughly 4 inches square and an inch thick, could be breached by someone with computer expertise, time and money.
Strickland said 20,000 state employees had signed up for identity-theft protection as of Tuesday night, and there had been no indications that someone had attempted to use their personal information.
The state is paying more than $700,000 to provide all state employees with identity-theft protection services and to hire an independent computer expert to review what data the tape contained. Officials said they would extend identity-theft protection services to the people in the categories announced Wednesday.
The tape was stolen June 10 out of the unlocked car of a 22-year-old intern who had been designated to take the backup device home as part of a standard security procedure. The governor has since issued an executive order ending the practice of employees taking backup devices home for safekeeping.
He also mandated a review of how state data is handled.