DuckCorp Dico

Found one definition

1.                 From The Jargon File (version 4.4.7, 29 Dec 2003):
                   
   
   
                   
                     
   mockingbird
    n.
       Software that intercepts communications (especially login transactions)
       between users and hosts and provides system-like responses to the users
       while saving their responses (especially account IDs and passwords). A
       special case of Trojan horse.