Source : Webster's Revised Unabridged Dictionary (1913)

Disservice \Dis*serv"ice\, n. [Pref. dis- + service: cf. F.
   desservice.]
   Injury; mischief.

         We shall rather perform good offices unto truth than
         any disservice unto their relators.      --Sir T.
                                                  Browne.

Source : WordNet®

disservice
     n : an act intended to help that turns out badly; "he did them a
         disservice" [syn: {ill service}, {ill turn}] [ant: {service}]