Quest Diagnostics, one of the largest medical laboratory companies in the United States, said an unauthorised party accessed its Quanum Lab Services Manager system and may have viewed certain patient records, according to a regulatory filing reported by the Associated Press.

The company said it discovered the incident on Wednesday, October 21, and disclosed it on Thursday. The Quanum platform is used by some clients to place test orders and to receive or look up results.

Quest said it started its cybersecurity incident-response procedures, notified federal law enforcement and brought in outside cybersecurity specialists. How many patients are affected, and exactly which records were involved, remain unknown while the investigation continues.

The company said the incident has not materially disrupted its business operations or its ability to serve patients, and it has not publicly identified how the intruder got in.

Quest also said its investigation does not connect this breach to the PHP security flaws disclosed earlier this week. Patients and clinics that use Quest services should watch for official updates from the company as the review continues.