The Hive ransomware group posted on its darkweb site that it has stolen 850,000 patient records from the Partnership HealthPlan of California, VentureBeat reported March 29.
The ransomware group posted March 29 that it had breached the health plan's systems, taking information such as names, Social Security numbers and addresses.
The group also claimed it has taken 400GB of stolen files from the organization's server.
Partnership HealthPlan of California, which has more than 618,000 members in Northern California, issued a warning March 24, stating that it became aware of anomalous activity on its computer systems, which has taken down its phone lines and website.
The warning did not mention a ransomware attack or Hive.
It is currently conducting an investigation into the matter and is working to restore its systems, according to a statement posted online.
Hive, which is known to target the healthcare industry, attacked Memorial Health System, which has hospitals in Ohio and West Virginia, in August 2021, and Franklin, Ind.-based Johnson Memorial Health in October 2021.
The post from the ransomware group has yet to be confirmed.