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[timsandtoms]

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[nls]

There is no sane way to do this on a FAT partition (what rockbox uses) and since we do not have any control over how the partition is presented to a computer it wouldn't work. If they are intended for use on a computer you could just use some file encryption on them. Or just buy your brother his own rockboxed player

[Chronon]

You can mark directories (or files) as hidden from your computer.  These will only display in Rockbox's file browser if the View Files settings is set to "All".