The insurance company said Thursday it was offering identity theft protection to the 41,437 policy holders affected.
Unity says the hard drive contains the Unity member number, date of birth, city of residence, name of prescribed drug, and date of service, if any.
It says the hard drive does not contain the name, street address, Social Security Number, credit card, banking or financial information of any Unity member.
Affected members are being notified by mail.
Unity says it has no reason to believe the hard drive was stolen to gain access to member information or that any information has been accessed or misused.
Police are investigating.