The UnitedHealth Group cyberattack on its Change Healthcare unit — claimed by the Blackcat ransomware group — ultimately affected about 192.7 million people, according to the U.S. Department of Health and Human Services. This is now confirmed as the largest healthcare data breach in U.S. history, exceeding the company’s earlier estimate of 190 million. The February 2023 breach disrupted nationwide claims processing and exposed health insurance IDs, diagnoses, treatment details, Social Security numbers, and billing codes. Individual impact numbers vary by state.