The documents found with the employee contained the patients' names, dates of birth, reason for visit and in some cases Social Security numbers, according to a Detroit Free Press report.
After discovering the documents during an identity theft investigation, police notified DMC officials of the data breach. The hospital immediately revoked the employee's access to computer systems.
A DMC spokeswoman said the employee is no longer with the hospital, but could not specify the person's former position, when the document discovery occurred or whether the patients' identities were used.
The Secret Service is leading the investigation into this data breach, and a local detective is on the case as part of the Southeast Michigan Financial Crimes Task Force.
The hospital is offering free credit monitoring to all affected patients.
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