Source : Webster's Revised Unabridged Dictionary (1913)

Harmful \Harm"ful\, a.
   Full of harm; injurious; hurtful; mischievous. `` Most
   harmful hazards.'' --Strype. --{Harm"ful*ly}, adv. --
   {Harm"ful*ness}, n.

Source : WordNet®

harmfully
     adv : in a detrimental manner [syn: {detrimentally}, {noxiously}]
           [ant: {harmlessly}]