If you can‘t unlock the Security & Privacy pane, make sure you‘ve set an admin password

You can't unlock the Security & Privacy pane if the admin account you're using has a blank password. Use these steps to set a password for the administrator account you want to use:

1. From the Apple menu, choose System Preferences.
2. Choose View > Users & Groups.
3. Select the admin user who currently has a blank password from the list of users in the preference pane.
4. Click the Change Password button.

   

5. Leave the Old Password field blank.
6. Enter a password in the New Password and Verify fields.
7. Enter a password hint.
8. Click Change.

You should now be able to use this admin account to unlock the Security & Privacy pane.