The nation's largest online forum, 2channel, draws millions of people ranging from the benign to the malignant, from police hunting criminals to politicians and corporations keeping their ears to the rail of public opinion.
Key to 2channel's power, and gravitational pull, is its anonymity. Its users can be frank, slanderous, even criminal.
Police use 2channel to combat crimes, especially posted threats. When they come upon such malevolence, they solicit IP addresses and other information on the parties involved.