Is warning people about a man who is known to commit evil openly regarded as backbiting?
Question

                Is warning people about a man who is known to commit evil openly, and is known to people for that, regarded as backbiting that people will be questioned about on the Day of Resurrection?.
Praise be to Allah.
    If the situation is as described and he mentions him so as to 
    warn people against his evil so that those who do not know about him will 
    not be deceived by him, it is permissible, but if it is only done for fun 
    and to pass the time and so on then it is not permissible. 

    And Allaah is the Source of strength. May Allaah send 
    blessings and peace upon our Prophet Muhammad and his family and companions. 
    End quote. 

    Standing Committee for Academic Research and Issuing Fatwas