Trolls are, unfortunately, ubiquitous on the Internet. Trolls go back to the days of UseNet, but they are still alive and well today in discussion forums and blog post comment threads. The troll is someone who engages in misbehavior online in order to elicit reactions, often, in hopes of angering/hurting/upsetting the unwary or naive user. Typically trolls will deliberately insult other posters and community members, post inflammatory text, or appear obtuse in order to elicit annoyed responses, all in hopes of gaining attention. Trolls engage in trolling. To an Internet troll, any attention is rewarding. The troll engages in online trolling in hopes of damaging the community, and obtaining attention, and hence amusement; thus the response of an online community is very often advice to other members: Don't feed the trolls. That is, don't reward them with any attention at all. This often starves and silences trolls, and they become bored and leave.

Etymologically, the concepts and usages of troll and trolling online derives from two unrelated words in English; a noun troll, and a verb to troll.

The Noun

From Old Norse; a mythological creature associated with bridges, magic, and luring people to their doom. The root of the word in Old Norse has to do with magic and charms/spells. Trolls in folklore are often to be found lurking under bridges, where they lure unwary travelers to their death (and consume goats, cows and sheep).

The noun troll was borrowed into English twice; first, directly from Old Norse into Old English as Troll; second from the dialect of English spoken on the Shetland Islands, which was inhabited by Norse speakers. Troll became trow.

The Verb

The verb to troll was stolen borrowed from Old French, but it is ultimately Germanic origin (Middle English trollen, to wander about, from Old French troller, of Germanic origin). Troll the verb has to do with repetitive motion, walking back and forth, or in a circle, or the sort of repetitive motion associated with trolling in fishing.

The Internet use of troll, which combines the verb and the noun—a person who repeatedly misbehaves. In terms of online use, and the behavior of trolls, and how to prevent and control them, Trolls: A Guide is an excellent resource. A fairly recent technique of online trolls is concern trolling; that's when a poster enters a discussion that is fairly calm and claims to be "supporting" the overall discussion but states that he or she has "concerns." In actuality the concern troll is there because they oppose the prevalent view, and wants to create dissent, often for amusement. A concern troll then proceeds to foment doubt, and hostility, by expressing "doubt," or "worry" or "concern" that is not genuine. An example of concern trolling would be to insert comments in a serious discussion about racial bigotry regarding the status of red heads as a minority group.