At a minimum, any license files and profile XMLs (as well as any custom macros, screen sets, or brains used by those profiles) should be backed up. In practice, it may be easier to keep a current backup of the entire Mach3 directory as this ensures everything necessary to rebuild the system should be available in the event of a catastrophic failure. The definition of a current backup is one that has been done after any permanent changes have been made to the software to alter it from its previous state. This includes such things as changes to any licenses, macros, screen sets, brains, or plugins as well as the modification of any configurations. We recommend using a USB flash drive or some other portable storage device as the backup media.