Astrana Health (ASTH) said in a regulatory filing Wednesday that certain confidential information maintained on its servers may have been accessed after its Astrana Health Management subsidiary detected unusual activity in its systems.

Investigation is ongoing, but Astrana has determined that the incident is material due to the potential confidential and sensitive nature of the data involved, according to the filing with the US Securities and Exchange Commission.

Astrana said the incident involved social engineering attempts in which threat actors impersonating Astrana employees and spoofing Astrana's corporate telephone number contacted some employees to get access to its systems.

The company said its cybersecurity team responded to the unauthorized activity, launched an investigation, and engaged a third-party digital forensics firm, while notifying law enforcement and regulators.

The company's shares were down past 7% in premarket activity Wednesday.