The Collaborative International Dictionary of English v.0.48:

Attack \At*tack"\, v. t. [imp. & p. p. Attacked; p. pr. & vb.
   n. Attacking.] [F. attaquer, orig. another form of attacher
   to attack: cf. It. attacare to fasten, attack. See Attach,
   Tack a small nail.]
   1. To fall upon with force; to assail, as with force and
      arms; to assault. "Attack their lines." --Dryden.
      [1913 Webster]

   2. To assail with unfriendly speech or writing; to begin a
      controversy with; to attempt to overthrow or bring into
      disrepute, by criticism or satire; to censure; as, to
      attack a man, or his opinions, in a pamphlet.
      [1913 Webster]

   3. To set to work upon, as upon a task or problem, or some
      object of labor or investigation.
      [1913 Webster]

   4. To begin to affect; to begin to act upon, injuriously or
      destructively; to begin to decompose or waste.
      [1913 Webster]

            On the fourth of March he was attacked by fever.
                                                  --Macaulay.
      [1913 Webster]

            Hydrofluoric acid . . . attacks the glass. --B.
                                                  Stewart.
      [1913 Webster]

   Syn: To Attack, Assail, Assault, Invade.

   Usage: These words all denote a violent onset; attack being
          the generic term, and the others specific forms of
          attack. To attack is to commence the onset; to assail
          is to make a sudden and violent attack, or to make
          repeated attacks; to assault (literally, to leap upon)
          is to attack physically by a had-to-hand approach or
          by unlawful and insulting violence; to invade is to
          enter by force on what belongs to another. Thus, a
          person may attack by offering violence of any kind; he
          may assail by means of missile weapons; he may assault
          by direct personal violence; a king may invade by
          marching an army into a country. Figuratively, we may
          say, men attack with argument or satire; they assail
          with abuse or reproaches; they may be assaulted by
          severe temptations; the rights of the people may be
          invaded by the encroachments of the crown.
          [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

attacked \at*tacked"\ adj.
   affected by disease.

   Syn: infected.
        [WordNet 1.5]