When records are expunged, they are sealed. They are not destroyed. Law enforcement officers, prosecutors, judges, prison officials, ect. are still allowed to look at them. If you apply for certain jobs for which your record would be important, your employer can look at the expunged records (for example, if you applied for a job at a nuclear power plant).
When your records are sealed, they are removed from public observation. For example, the Clerk of Courts removes your records from his public indexes of cases, and from his public files.
However, if a private company found out about your record before it was sealed, then that information is out and the private companies can display it or sell it.
In California, your privacy is protected by these laws:
1. The Fair Credit Reporting Act (FCRA).
2. The Driver’s Privacy Protection Act.
3. The American with Disabilities Act (ADA).
4. Different states have different legal frameworks, such as the Investigative Consumer Reporting Agencies Act which exists in California.
You can perform a free background check.