Backbone has multiple options for synchronizing security level field.
The synchronization user needs the "Set Issue Security" permission to perform this mapping. Check the Managing project permissions page for details.
Same security level to same security level
If you want to synchronize all issues to the same security level in both instances, simply select the Security Level Passthrough Mapping option.
If one synchronization partner tries to synchronize a security level with an instance without a security level with the same name, the synchronization won't work. To avoid this verify that all the security levels have the same name in the partner instance when the synchronization is started.
Specific security level to specific security level
You can synchronize specific security levels to other specific security levels. For example, you can synchronize issues with security level 'Only reporters' in Project A to security level 'Only testers' in Project B.
To do so, select the Security Level Correlation Mapping setting, and in the Security level mapping section, click Add Entry to select the security level you want to synchronize. The security levels are mapped according to the number they are assigned to – so the security level assigned to number 1 on the left side will be synchronized to security 1 on the right side.
You must also select a default security level for the issue to be mapped to in case you are synchronizing a security level that you haven't created a mapping for. You can do this using the Default Security Level dropdown.
Synchronize security level to a free text field
You can synchronize a security level name to a free text field. The mapping can only be unidirectional, because Backbone doesn't support parsing the security level field from the other instance.
To setup this mapping select security level and a text field. This will automatically select the Security Level to Text Mapping option.
The synchronization user needs to access the security levels it is expected to sync, otherwise it will not be able to detect changes on the issue with a security level that excludes it from selecting them.