Abstract: An article surveillance marker suitable for use on computer magnetic data disks is disclosed in which the marker, a length of low coercivity, high magnetic permeability ferromagnetic material is integrally formed onto the data disk preferably so as to serve as the concentricity determining factor of the disk, whereby attempted removal or override of the marker renders the disk from unauthorized reproduction. A disk drive sytem is also disclosed with a built-in interrogation zone and write inhibit circuit that insures data originating from the host computer or copied from another marker-protected disk can only be written onto a disk having a marker-protected disk.