A cyberattack on UnitedHealth Group Inc. that paralyzed the US health-care system last year, snarling billions of dollars in payments for doctors and hospitals, also exposed sensitive data from 190 million Americans.

The updated tally extends the scope beyond what was previously described by company Chief Executive Andrew Witty.

Large-scale attacks on health providers expose the data of millions of Americans each year. Consumers must remain vigilant, experts say.