Authorities in the United States, as well as in the United Kingdom and in Ireland, have arrested five suspected hackers affiliated with Lulz Security, more commonly known as “LulzSec,” a group of so-called hacktivists. Among those arrested is Hector Xavier Monsegur, the suspected leader of the group. Monsegur, who went by the nickname “Sabu,” actually cooperated with the FBI to help track and arrest the other LulzSec members. In this way, the FBI is reusing an old, but effective, method from its own playbook. “This is how the FBI eventually took down the Mafia,” said Rob Rachwald, director of strategy for Imperva.