Since 2011, the collective hacking group, Anonymous and LulzSec were targeting both Government and law-enforcement websites of U.S. and UK, by their own DDoS attack tactics. British intelligence agency GCHQ used their own weapon against them. The same DDoS technique the hackers use to take down government, political and industry websites, including the Central Intelligence Agency (CIA), Federal bureau of Investigation (FBI), the Serious Organized Crime Agency (SOCA), Sony News International and Westboro Baptist Church.
Source: https://thehackernews.com/2014/02/british-intelligence-agency-ddosed.html