In another forum I frequently post in, the term 'a troll' has come to mean a person that comes with remarks of a negative nature about the main forum's topic. So, for example, in a forum dedicated to a PC game, such a person expresses criticism, makes complaints or gripes that are totally unjust and only serve the purpose of spreading negative attitudes towards the game and spoil the forum's atmosphere.
Since the word 'troll' in this context has become an element of the internet forums' jargon, its meaning may vary a bit from site to site. The meaning I've just given is one that I've come across.
Hope the above helps.
All the best,
- For Teachers