Source : WordNet®

mockingbird
     n : long-tailed gray-and-white songbird of the southern United
         States able to mimic songs of other birds [syn: {mocker},
          {Mimus polyglotktos}]

Source : Free On-Line Dictionary of Computing

mockingbird
     
        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}.
     
        [{Jargon File}]