LockXLS Runtime blocks access to hidden data in spreadsheet. Only VBA macro from protected spreadsheet has permission to access this data. If you need to work with this data from your external application - select Project Options | Excel Object Model protection options ... | Allow to access to data on hidden sheets option. Hidden data could be accessed only after providing Unlock Code. It will identify application which has access to hidden data.
You can find more information and sample VBA code for this option here.