Almost 30,000 Kaiser Permanente employees working in northern California will be receiving notification letters this weekend informing them of a major security breach that has taken place causing their personal information to be compromised.

The information includes names, addresses, Social Security numbers, and dates of birth for the Kaiser employees.

A press release issued by Kaiser indicated police officers have arrested a person who had computer files with Kaiser human resources information, and that person was arrested in late December.  

Mia Garza was arrested by San Ramon police on December 23 and now faces two charges of receiving stolen property, two counts identity theft, and two counts of forgery.  It remains unclear how Garza came to possess the Kaiser files, and police officials haven't speculated how she came into possession of the computer data.

"We immediately launched an internal investigation and are working to determine the source of this breach, and we are working closely with law enforcement in their investigation," the company said in a statement. "To our knowledge, only a handful of employees have reported identity theft."

The company isn't sure how the data breach occurred or how many employees have been affected, except for a "handful."  Kaiser patients haven't been compromised, and individual medical records are still secure.

Kaiser is now offering northern California employees one year of free credit monitoring for all those affected.  The insurance company is recommending all employees place a fraud alert on their credit lines and to order copies of credit reports as soon as possible.

When companies announce data breaches this size, it’s normally customers and patients who have been compromised, not employees.