Quest paused access to the system while it investigates, and told customers they can use paper requisitions in the meantime. It pledged to have the platform back up by Friday, and said no other part of the business was affected, though several other systems were paused while investigators probe the breach. The company has notified federal law enforcement and is working with external cybersecurity experts.

The scale could be significant. Quest says Quanum is used by around half a million clinicians across North America, and the platform stores patient health records along with diagnostic and billing data. Quest is one of the largest clinical laboratory companies in the US, serving half of the country's doctors and hospitals and roughly one in three American adults each year.

It is not the company's first brush with data theft. In 2016, a breach exposed lab results and contact details for about 34,000 people, and in 2019 the records of about 11.9 million Quest patients were caught up in a hack at its billing collections vendor, American Medical Collection Agency. Quest also confirmed to the Associated Press that this incident is unrelated to the recent PHP vulnerabilities that have been causing disruption elsewhere.