The February hack at UnitedHealth's tech unit Change affected the personal information of 100 million people, the U.S. health department's website showed, making it the largest healthcare data breach in the country.

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

The ransomware attack against UnitedHealth-owned Change Healthcare was so large that impacted Americans are being notified on a “rolling basis.” Earlier this year, Change Healthcare, a subsidiary of UnitedHealth Group (UHG) and key player in the U.