When talking about internet trolls, they are people who log on as bad names, disrupt threads, follow other posters around and harass them on the boards, or post the same things or questions again and again and again, even after people told them the answer to their questions or have told them to stop.
Basically trolls are people who are disruptive and cause trouble for mods in that they get reports about them and we have to take care of it in the back.
An Internet troll, or simply troll in Internet slang, is someone who intentionally posts controversial or contrary messages in an on-line community such as an on-line discussion forum or group with the intention of baiting users into an argumentative response.[1]
If you are talking about the ugly dolls with spiky hair that is fluorescent colors with gems in their belly buttons, that is a different thing.
The nicer trolls live under rainbows too, but they are real trolls, not internet trolls.
I know on other boards, if a user changes their name or re-registeres under a different name the mods can tell.
I'm on another board and they immediately ban anyone who has more than one login on the same computer ID unless you let them know in advance you are signing up another ID, like for a husband or child, etc