Ringleaders urged volunteers to download software that flooded Web sites with useless Internet traffic, ultimately causing may of them to come grinding to a stop. Other victims included the Web sites of WikiLeaks critic Sarah Palin and the Swedish Prosecutor's Office, which is pursuing sex charges against WikiLeaks founder Julian Assange.

The FBI investigation centers on the IRC servers, used to coordinate the attacks. The FBI initiated the investigation on Dec. 9 after PayPal provided them with the Internet Protocol addresses of eight IRC servers used in by the group.

On Dec. 9, Dutch police .

The IDG News Service