The catalogue was hidden by placing a VDU21 control code in the last character of the title string. This effectively disables VDU output. In addition the first file name was !AVP. The control codes cleared the screen, switched off printer output and disabled the VDU.
Additionally the disk had only the first 20 tracks formatted, thus preventing *BACKUP.
*COPY *.* was prevented by the control codes in the first file.
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