[andyjpb]

Yes.

If there's an illegal number X and I give you a number Y with the intention that you obtain X from it by some transform then Y is also illegal because I "tainted" it when I did the original transformation from X.

If I just need Y (or X) for some operation that's not related to the "illegality" then those numbers are not illegal.

The essay that droffel linked to explains this very well.