site chattr +h "dir" "M !*"
dunno if you need those quotes at the end, however.
in your example you had * !M , which first allows anyone to see and then denies masters, but since you first allow everyone that !M doesnt make much ;p
if you only want admins to be able to see you should have M !* (allows those with M flag to see and denies [!] everone else).
hope this helps you
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