Hundreds of thousands of Americans are now at risk of identity theft and fraud after a major data breach at a human resources firm.

In a new filing with the Office of the Maine Attorney General, Maryland-based Kelly Benefits says it has discovered a significant cybersecurity incident impacting 413,032 people.

The company says an internal investigation revealed that an unknown entity gained unauthorized access to its database and stole sensitive customer information, including names, dates of birth, Social Security numbers, tax ID numbers, medical and health insurance records and financial account datasets.