The worldwide hacktivist juggernaut Anonymous has been committed to dishing out vigilant, ironic justice to evildoers ever since 2008. Inflicting damage with any mix of doxing (tracing someone online to gather sensitive info - SSN, phone numbers, address, credit card info, etc.), Distributed Denial of Service (DDoS) attack or takedown (flooding a site with ungodly traffic), the hackivists known only by their ubiquitous Guy Fawkes masks are a band of protestors you don't want to cross.
With their famous salutation of "Knowledge is free. We are Anonymous. We are Legion. We do not forgive. We do not forget. Expect us.," Anonymous has dealt swift, painful justice to some of the world's most powerful (and controversial) entities.