U.K.-based healthcare billing software maker Craneware is responding to a cyberattack in which hackers stole a “significant volume” of customer data from its systems, the company said on Monday.

The company said the hackers appear to have been expelled from its systems, but its investigation into the breach is ongoing, according to a statement filed with the London Stock Exchange.

Craneware’s flagship accounting and billing software is used by thousands of clinics, hospitals, and pharmacies across the United States. The company did not say exactly what kinds of data were taken in the breach, only noting that a “percentage” of employee data, customer data, and partner records had been exfiltrated.

The company, whose software helps healthcare providers bill patients for services, handles large amounts of medical records and patient data on behalf of its customers. When it bought Florida-based pharmacy software maker Sentry in 2021, Craneware said it gained access to the company’s 147 million patient records that had been collected over two decades.

Craneware CEO Keith Neilson did not immediately respond to TechCrunch’s questions about the incident, or if the hackers have contacted the company with any demands, such as a ransom.