Here's an interesting report (Daily Mail, but still) about a University of Manitoba study on online trolls. According to the study, trolling correlates "positively with sadism, psychopathy, and Machiavellianism." Sounds about right.
http://www.dailymail.co.uk/sciencetech/article-2559860/Online-trolls-really-ARE-horrible-people-researchers-Narcissistic-Machiavellian-psychopathic-sadistic.html