NEW YORK (CNNMoney) -- In the U.S. government's biggest crackdown to date on a hacktivist group calling itself "Anonymous," four leaders and one other activist were arrested Tuesday and charged with a computer hacking conspiracy. The U.S. Department of Justice also revealed Tuesday that it had snared the prime leader of an Anonymous offshoot group called LulzSec, which conducted a high-profile, two-month hacking rampage last summer against corporate and government targets. -snip- What particularly set the movement on edge was the conviction and apparent turning of the LulzSec leader Hector Xavier Monsegur, known by his hacker alias Sabu.