They are the bane of online communities, the destroyer of online games. Griefers are pests to the highest degree, but, as Wired argues, an essential and important part of the gaming experience. In a thoughtful feature dissecting griefer culture in the virtual world Second Life, one group of goons, the Patriotic Nigras (aka the PNs), are profiled and documented.
From the article:
Griefing, as a term, dates to the late 1990s, when it was used to describe the willfully antisocial behaviors seen in early massively multiplayer games like Ultima Online and first-person shooters like Counter-Strike (fragging your own teammates, for instance, or repeatedly killing a player many levels below you). But even before it had a name, grieferlike behavior was familiar in prehistoric text-based virtual worlds like LambdaMOO, where joyriding invaders visited "virtual rape" and similar offenses on the local populace.