From the New York Times:
It began with an impassioned, 5,000-word letter on one of the country’s most popular Internet bulletin boards from a husband denouncing a college student he suspected of having an affair with his wife. Immediately, hundreds joined in the attack.
“Let’s use our keyboard and mouse in our hands as weapons,” one person wrote, “to chop off the heads of these adulterers, to pay for the sacrifice of the husband.”
Within days, the hundreds had grown to thousands, and then tens of thousands, with total strangers forming teams that hunted down the student, hounded him out of his university and caused his family to barricade themselves inside their home.
Here.