If it is to your personal advantage to act unjust and the unjust act
will never be discovered, is it ethically permissible to act unjustly?

In my own ethical code, a wrong act certainly doesn't become right
just because it won't be discovered. I can't imagine any ethical code
in which the possibility of discovery is the determining factor of
whether or not an act is ethical.

For some reason, this question reminds me of "if a tree falls in a
forest, and there's no one there to hear it, does it make any noise?"
Or its corollary: "If a man speaks in the forest, and no woman is
there to hear him, is he still wrong?"

"Character is doing what is right when no one is looking." - J.C. Watts

I agree. In my opinion, it is never all right to do what is wrong,
regardless of who will know or not.

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