A February cyberattack on a UnitedHealth subsidiary compromised the personal data of some one-third of Americans.

UnitedHealth, the largest U.S. health insurance provider, blamed a Russia-based ransomware gang for the huge data breach of U.S. medical data.

Data recently posted on a federal website shows the cyberattack earlier this year at a UnitedHealth Group subsidiary affected 100 million patients — apparently a U.S. record. The tally roughly matches the scope previously described by company Chief Executive Andrew Witty,