From "Mother Jones", interesting read about people we know:

http://www.motherjones.com/blue-marble/2014/02/internet-trolls-sadists-psychopaths-lulz?google_editors_picks=true

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In the past few years, the science of Internet trollology has made
some strides. Last year, for instance, we learned that by hurling
insults and inciting discord in online comment sections, so-called
Internet "trolls" (who are frequently anonymous) have a polarizing
effect on audiences, leading to politicization, rather than deeper
understanding of scientific topics.

That's bad, but it's nothing compared with what a new psychology paper
has to say about the personalities of so-called trolls themselves. The
research, conducted by Erin Buckels of the University of Manitoba and
two colleagues, sought to directly investigate whether people who
engage in trolling are characterized by personality traits that fall
in the so-called "Dark Tetrad": Machiavellianism (willingness to
manipulate and deceive others), narcissism (egotism and
self-obsession), psychopathy (the lack of remorse and empathy), and
sadism (pleasure in the suffering of others).

It is hard to underplay the results: The study found correlations,
sometimes quite significant, between these traits and trolling
behavior. What's more, it also found a relationship between all Dark
Tetrad traits (except for narcissism) and the overall time that an
individual spent, per day, commenting on the Internet.

In the study, trolls were identified in a variety of ways. One was by
simply asking survey participants what they "enjoyed doing most" when
on online comment sites, offering five options: "debating issues that
are important to you," "chatting with others," "making new friends,"
"trolling others," and "other."

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