Usually when I comment on anything over a month old, the original commenter raves at me for being "so late" and "this comment was made so long ago."
Anyway to answer your question, a troll simply says something to get an emotional response, preferably rage. A troll doesn't target a specific person. If you ignore them, they'll more likely than not move on, unless they like you or something.
A bully targets a specific person or group of persons, trying to get fear to arise from them. They will not go away, even if you ignore them. Some resort to violence, some don't.
What you mean though, is cyberbullying, yes? dA's rules for cyberbullying is constant harassment of a single person, including after they're blocked. That means that if they're blocked and they make a second account to harass them some more, or send a friend after them, THAT'S illegal and they can get banned. Trolls don't go to that level.
Hope that helped. (: