The Collaborative International Dictionary of English v.0.48:

Malefactor \Mal`e*fac"tor\, n. [L., fr. malefacere to do evil;
   male ill, evil + facere to do. See Malice, and Fact.]
   1. An evil doer; one who commits a crime; one subject to
      public prosecution and punishment; a criminal.
      [1913 Webster]

   2. One who does wrong by injuring another, although not a
      criminal. Opposite of benefactor. --H. Brooke. --Fuller.
      "Malefactors of great wealth." [1913 Webster +PJC]

   Syn: Evil doer; criminal; culprit; felon; convict.
        [1913 Webster]

WordNet (r) 3.0 (2006):

malefactor
    n 1: someone who has committed a crime or has been legally
         convicted of a crime [syn: criminal, felon, crook,
         outlaw, malefactor]

The Devil's Dictionary (1881-1906):

MALEFACTOR, n.  The chief factor in the progress of the human race.