Cyberattack disrupted systems at 13 McLaren hospitals and Karmanos cancer centers across Michigan.
McLaren Health Care in Michigan has begun notifying over 743,000 individuals that their personal and health data may have been compromised in a ransomware attack in August 2024.
The health system confirmed that unauthorised access to its systems began on 17 July and continued until 3 August 2024, affecting McLaren Health Care and its Karmanos Cancer Centers.
A forensic investigation concluded on 5 May 2025 revealed that files containing names, Social Security numbers, driver’s licence details, medical information, and insurance data were accessed.
Notification letters began going out on 20 June 2025, and recipients are being offered 12 months of complimentary credit monitoring and identity theft protection.
Although the incident has not been officially attributed to a specific ransomware group, industry reports have previously linked the attack to the Inc. Ransom group. However, McLaren Health Care has not confirmed this, and the group has not publicly listed McLaren on its leak site.
However, this is McLaren’s second ransomware incident within a year. A previous attack by the ALPHV/BlackCat group compromised the data of more than 2.1 million individuals.
Following the August 2024 attack, McLaren Health Care restored its IT systems ahead of schedule and resumed normal operations, including reopening emergency departments and rescheduling postponed appointments and surgeries.
However, data collected manually during the outage is still being integrated into the electronic health record (EHR) system, a process expected to take several weeks.
McLaren Health Care has stated that it continues to investigate the full scope of the breach and will issue further notifications if additional data exposures are identified. The organisation works with external cybersecurity experts to strengthen its systems and prevent future incidents.
The attack caused disruptions across all 13 hospitals in the McLaren system and affiliated cancer centres, surgery centres, and clinics. While systems have been restored, McLaren has encouraged patients to remain prepared by bringing essential documents and information to appointments.
The health system expressed appreciation for its staff’s efforts and patients’ patience during the response and recovery efforts.
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