You are forbidden to relate information about a person’s past misdeeds or the misdeeds of his family, even if you do not not intend to belittle him, and you will not cause the listener to think less of him, as he has now corrected his ways.

This is forbidden because a person is usually embarrassed of his misdeeds are recalled in his presence.  Hence, you might ultimately cause him anguish if the information becomes widely known. ~ Guard Your Tongue