Massachusetts medical services provider Onsite Mammography is notifying over 350,000 people that their personal and health information was compromised in a data breach.
The incident was discovered in October 2024 and involved unauthorized access to an employee’s email account, the firm reveals in a notification letter mailed to the impacted individuals.
Some of the emails in the compromised account’s inbox, Onsite says, exposed both personally identifiable information (PII) and protected health information (PHI).
A review of the exposed information that was concluded in February 2025 determined that names, Social Security numbers, dates of birth, driver’s license numbers, credit card numbers, and medical information such as mental and physical health or condition, and received care information was compromised.
“The investigation further revealed that the actor only had access to the email account and did not have access to any other systems within our network,” Onsite says.
The medical services provider notified the Maine Attorney General’s Office that 357,265 patients were impacted and that it is providing them with 12 months of free credit monitoring and identity protection services.
“Onsite has no reason to believe any information has been or will be misused as a result of this incident,” the healthcare organization said in a press release.
Operating under the Onsite Women’s Health brand, Onsite Mammography provides in-office breast health and imaging service nationwide, including 3D mammography, automated Whole-Breast Ultrasound, and risk assessment services.
“Onsite Women’s Health identified unauthorized access to one employee’s email account as a result of a phishing email. The incident was limited in scope, and there is no evidence that the information has been misused. We took immediate action, engaged cybersecurity experts, notified law enforcement and notified affected individuals. We remain fully committed to safeguarding patient privacy and data security,” Onsite told SecurityWeek in an emailed statement.
*Updated with statement from Onsite.
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