The contemporary use of the term first appeared on Usenet groups in the late 1980s. It is thought to be a truncation of the phrase trolling for suckers, itself derived from the fishing technique known as trolling. The word likely gained currency because of its apt second meaning, drawn from the trolls portrayed in Scandinavian folklore and children's tales; they are often ugly, obnoxious creatures bent on mischief and wickedness.
Wikipedia, do you use it?
http://en.wikipedia.org/wiki/Troll_Internet