One afternoon in the spring of 2006, for reasons unknown to those who knew him, Mitchell Henderson, a seventh grader from Rochester, Minn., took a .22-caliber rifle down from a shelf in his parents’ bedroom closet and shot himself in the head. The next morning, Mitchell’s school assembled in the gym to begin mourning. His classmates created a virtual memorial on MySpace and garlanded it with remembrances. One wrote that Mitchell was “an hero to take that shot, to leave us all behind. God do we wish we could take it back. . . . ” Someone e-mailed a clipping of Mitchell’s newspaper obituary to MyDeathSpace.com, a Web site that links to the MySpace pages of the dead. From MyDeathSpace, Mitchell’s page came to the attention of an Internet message board known as /b/ and the “trolls,” as they have come to be called, who dwell there.

/b/ is the designated “random” board of 4chan.org, a group of message boards that draws more than 200 million page views a month. A post consists of an image and a few lines of text. Almost everyone posts as “anonymous.” In effect, this makes /b/ a panopticon in reverse — nobody can see anybody, and everybody can claim to speak from the center. The anonymous denizens of 4chan’s other boards — devoted to travel, fitness and several genres of pornography — refer to the /b/-dwellers as “/b/tards.”

Measured in terms of depravity, insularity and traffic-driven turnover, the culture of /b/ has little precedent. /b/ reads like the inside of a high-school bathroom stall, or an obscene telephone party line, or a blog with no posts and all comments filled with slang that you are too old to understand.

Something about Mitchell Henderson struck the denizens of /b/ as funny. They were especially amused by a reference on his MySpace page to a lost iPod. Mitchell Henderson, /b/ decided, had killed himself over a lost iPod. The “an hero” meme was born. Within hours, the anonymous multitudes were wrapping the tragedy of Mitchell’s death in absurdity.

Someone hacked Henderson’s MySpace page and gave him the face of a zombie. Someone placed an iPod on Henderson’s grave, took a picture and posted it to /b/. Henderson’s face was appended to dancing iPods, spinning iPods, hardcore porn scenes. A dramatic re-enactment of Henderson’s demise appeared on YouTube, complete with shattered iPod. The phone began ringing at Mitchell’s parents’ home. “It sounded like kids,” remembers Mitchell’s father, Mark Henderson, a 44-year-old I.T. executive. “They’d say, ‘Hi, this is Mitchell, I’m at the cemetery.’ ‘Hi, I’ve got Mitchell’s iPod.’ ‘Hi, I’m Mitchell’s ghost, the front door is locked. Can you come down and let me in?’ ” He sighed. “It really got to my wife.” The calls continued for a year and a half.

In the late 1980s, Internet users adopted the word “troll” to denote someone who intentionally disrupts online communities. Early trolling was relatively innocuous, taking place inside of small, single-topic Usenet groups. The trolls employed what the M.I.T. professor Judith Donath calls a “pseudo-naïve” tactic, asking stupid questions and seeing who would rise to the bait. The game was to find out who would see through this stereotypical newbie behavior, and who would fall for it. As one guide to trolldom puts it, “If you don’t fall for the joke, you get to be in on it.”