The agency says its internal system was immediately shut down to ensure the Orange County criminal justice system continued to function properly.
The district attorney's office says it was able to isolate the hacked-portion of its network and immediately coordinated with law enforcement.
It's still unclear if any information was compromised.
"OCDA immediately began working with a third-party expert to assist in identifying any vulnerabilities in our information technology systems," the DA's office said in a statement. "OCDA staff has been working around-the-clock to ensure continuity of operations with our critical services and functions."
The breach is now under investigation by the FBI.