OOfficials are investigating a security and privacy breach affecting 900 patients who were treated at the Los Angeles County - USC Medical Center 's mental health facility . The breach was discovered April 3 during a search of the home of a nurse who was employed at the Augustus F. Hawkins Mental Health Center , said Michael Wilson , a spokesman for the Los Angeles County Department of Health Services . The investigation was not related to county business , he said . The nurse , whose name was n't released , allegedly stole documents containing patients ' names , medical and insurance information , birth dates , Social Security numbers , diagnoses and other personal information . The nurse has since resigned and is no longer working with the hospital , Wilson said . Patients treated at the Hawkins facility between 2011 and 2015 were affected by the breach , he said . It was unclear whether any of the patients ' information was misused . A county team assigned to investigate breaches under the Health Insurance Portability and Accountability Act is conducting an internal probe . County officials have notified the patients by letter as well as the California Department of Public Health . A notice of the breach was also posted on the hospital 's website . The Los Angeles County district attorney 's Cyber Investigation Response Team is looking into the breach , spokeswoman Jane Robison said . Details about the breach were not released because the case is under investigation . County health employees must undergo privacy training as well as follow a series of procedures designed to protect patient confidentiality . " Despite all of these procedures , these incidents still happen , " Wilson said . Meanwhile , free credit monitoring services of up to a year were offered to the affected patients . ;