Personal information on 72 worker's compensation claimants was stolen from Sentry Insurance and later sold over the Internet, the company said.
The data sold included names and Social Security numbers but not medical records, Sentry said. Data on an additional 112,198 claimants was also stolen but there is no evidence it was sold, the company said.
Sentry said it notified everyone affected and was providing credit monitoring services to help prevent fraud.
The thief was "a lead programmer/consultant with a nationally recognized computer contractor" hired by Sentry, based in Stevens Point, company officials said Friday.
Sentry said the consultant was arrested outside Wisconsin by the Secret Service and faces federal felony charges.
Secret Service representatives did not immediately return a call from The Associated Press seeking comment Saturday.
Mary Weller, corporate communications director for Sentry, would not say where or when the arrest occurred, or give details about when the theft occurred or how it was discovered.
It was the first theft of claimants' personal data from Sentry, Weller said.