Trolls' characteristicae

1) They have a lot of free time, they are mostly lonely people.
2) They often ingratiate themselves to a person or two on the group and use them to stay in the group. They may protest with these "friends" that their right to free speech is being curtailed.
3) They sometimes use "socketpuppets", i.e. fake identities that may be used to sustain, or to inflame the troll's position or theory or attack. At times the socket puppets' names are anagrams or similar to the troll name. Thus a troll may engage in artificial conversations with himself. However impersonating multiple people is frowned upon by the more able trolls and is considered the lowest of the possible troll tactics.



are trolls useful? ...Yes...
Yes (as somebody wrote long ago), much like hyenaes: if a messageboard is strong and vibrant, with healthy ideas and intelligent discussion among posters, then these tend to be too interested in what is going on to pay much attention to the trolls. However, once a forum begins to show signs of decay - usually due to bickering amoung the regular visitors - then the trolls run rampant and it is only a matter of time before the forum disintegrates.
Moreover: "Trolls remind us that this is not private space. Lurkers are everywhere but it is easy to forget that. Chatting away on a thread with an old buddy it is easy to reveal personal details about one's life that you might not really want public. Trolls remind us that in a public forum anyone can read what we write."

Moreover, as we have seen in Trolls and Schopenhauer and with the debunking example above, trolls DO deliver us many useful findings about "Eristic Dialectic stratagems". Findings that we can easily apply outside the world of Usenet :-)

...and no
This said, trolls and (even more) shills are very often de facto and/or de jure just lackeys of the commercial powers that be. What all trolls have in common is that they flood newsgroups with inappropriate material in an effort to suppress discussion they don't want taking place. If it were radio, you would call it "jamming" and everybody would agree it was censorship. But on Usenet or on messageboards, the effect is more subtle and the mechanism more complex (involving user interface limitations of newsreading software) so it hasn'e been widely recognized yet. Some of the most determined destroyers are professionals trollers connected to people that stand to lose if a specific Usenet newsgroup (or any given specific messageboard) proves to be a viable alternative to the(ir) controlled channels of mass communications.
Let's see how to (try to) destroy them...

(stolen without permission from Fr***a+) sorry!