The Los Angeles County Department of Health Services disclosed a data breach after thousands of patients' personal and health information was exposed in a data breach resulting from a recent phishing attack impacting over two dozen employees.

This integrated health system operates the public hospitals and clinics in L.A. County (the most populous county in the United States) and is the second largest public health care system in the country after NYC Health + Hospitals. 

As revealed in data breach notifications sent to potentially affected individuals, 23 employees had their mailboxes compromised after their credentials were stolen in a February attack. 

As a result, the attackers gained access to patients' personal and health data stored in the employees' e-mail inboxes.

"DHS conducted an administrative review and determined that approximately 6,085 individuals' information may have been impacted," L.A. County Health Services reported in a statement.

"Between February 19, 2024, and February 20, 2024, DHS experienced a phishing attack. Specifically, a hacker was able to gain log-in credentials of 23 DHS employees through a phishing e-mail," the notifications also revealed.

"In this case, the DHS employees clicked on the link located in the body of the e-mail, thinking that they were accessing a legitimate message from a trustworthy sender."

Documents and e-mails in the compromised mailboxes included a combination of patients' personal and health information, including:

• first and last name, date of birth, home address, phone number(s), e-mail address, medical record number, client identification number, dates of service
• medical information (e.g., diagnosis/condition, treatment, test results, medications),
• and/or health plan information.

Affected individuals may have been impacted differently, and the data stored in the breached e-mail inboxes did not include Social Security Numbers (SSNs) or financial information.

After discovering the breach, L.A. County Health Services disabled the impacted e-mail accounts, reset and re-imaged the compromised employees' devices, and quarantined all suspicious incoming e-mails. It also circulated awareness notifications to all employees, reminding them to always be vigilant when reviewing e-mails, especially those with attachments or links.

The health system will also notify the U.S. Department of Health & Human Services' Office for Civil Rights, the California Department of Public Health, and other relevant agencies of the data breach.

Additionally, even though no evidence was found during the investigation that the attackers accessed or misused the exposed personal and health information, L.A. County Health Services advises affected patients to contact their healthcare providers to verify the content and accuracy of their medical records.

Update April 26, 05:20 EDT: Added L.A. County Health Services statement.