Updated

A woman posing as a health care worker at a Billings hospital accompanied doctors on multiple patient checks, leading Montana health officials to warn employees at other facilities to be on the lookout for an impostor wearing scrubs or a lab coat.

The woman has breached security at Billings Clinic an undetermined number of times, prompting Billings' other hospital, St. Vincent Healthcare, to circulate surveillance photos and a warning memo to employees.

"She is a talented liar and will invent all sorts of stories as to who she is and what she is doing," Curtis Harper, St. Vincent's regional director of Public Safety, Emergency Management and Forensic Investigation, said in the memo. "She accompanied physicians as they checked on patients on a number of occasions at Billings Clinic."

The woman has claimed to be a physician assistant student, a nurse practitioner student, a neonatal intensive care unit nurse and even the director of nursing, Harper wrote. She has some medical background and was able to speak as though she belongs in a hospital, he said.

The woman's motivation, the time period she accessed Billings Clinic and whether she had one-on-one contact with patients is unclear.

Billings Clinic notified RiverStone Health, Yellowstone County's public-health agency, of the fake nurse on Thursday, said RiverStone director of communications and advocacy Barbara Schneeman.

"We're watching," Schneeman said. "We are definitely mindful of the situation. We are keeping eyes and ears open."

Julie Burton, director of communications of Billings Clinic, said the hospital also informed police, and officials are working closely with officers and the Yellowstone County Attorney's office.

Billings police Chief Rich St. John said an investigation is underway but no arrest has been made.

The Billings Gazette reports hospital officials named the woman, but St. John declined to confirm her identity.