A person or group of people typically performing as a single avatar in an online environment (or a participant in an online forum), who participates in the activity of griefing: deliberate attempts to disrupt activities or cause distress to others. Griefers often use malicious software: for example, by initiating automated programs that replicate themselves, which can overload servers and cause whole virtual worlds to crash. The antics of a griefer can range from mildly annoying to sociopathic. Compareflaming; troll.
http://www.wired.com/gaming/virtualworlds/magazine/16-02/mf_goons Julian Dibbell on griefers
Subjects: Media Studies.