GRAND RAPIDS, Mich. (WOOD) — More than 33,000 Michigan Medicine patients may have had their personal health information exposed after a phishing scam fooled four employees earlier this year.

University of Michigan Health-West is one part of the Michigan Medicine health care system. A spokesperson for the company said the exposed patients were only from the the system’s hospitals on the Ann Arbor campus, not U of M Health West.

According to a Thursday news release, a cyberattacker sent fraudulent emails in mid-August posing as Michigan Medicine. Four employees were fooled by the emails, entering their login information and following the multi-factor identification prompts, giving the hacker access to the employees’ email accounts.

Michigan Medicine discovered the phishing scheme on Aug. 23 and disabled the accounts to cut off the access. The health care group says there is no evidence that the hackers were looking for patient health information but data theft couldn’t be ruled out. Still, it is encouraging patients to keep a close eye on their medical insurance statements to look for any evidence of possible fraud.

The group reviewed which patients’ data could have been exposed. The review was finished Oct. 17. All potentially impacted clients or their representatives should have already been notified.

In the release, Michigan Medicine Chief Compliance Officer Jeanne Strickland apologized.

“Patient privacy is extremely important to us, and we take this matter very seriously. Michigan Medicine took steps immediately to investigate this matter and is implementing additional safeguards to reduce risk to our patients and help prevent recurrence,” Strickland stated.

Any concerned Michigan Medicine patients can call the company’s toll-free assistance line — 1.833.814.1736. The phone line is staffed from 9 a.m. to 9 p.m. Monday through Friday, except holidays.

Michigan Medicine includes five hospitals, 125 clinics and home care operations that handle more than 2.3 million outpatient visits each year, along with the University of Michigan’s Medical School.