New Edward Snowden leaks surfaced today, describing how GCHQ, the British signals inelligence agency, mounted an online attack on the hacktivist collective known as Anonymous in September 2011. The slides, obtained exclusively by NBC News, indicate UK cyberspies used a denial of service attack (DoS) in 2011 to force a chatroom used by the Anonymous collective offline.

Besides Anonymous, LulzSec, the A-Team and the Syrian Cyber Army are listed as hacktivist groups GCHQ was concerned about.

The documents also indicate how GCHQ's Joint Threat Research Intelligence Group (JTRIG) spied on and communicated with chatroom (IRC) users to identify hackers who had stolen information. The agents have tricked a hacker nicknamed P0ke who claimed to have stolen data from the US government. According to NBC, P0ke was never arrested despite GCHQ learning his true name.

But the leaks indicate others were imprisoned as a result of JTRIG operations. GZero was sentenced to two years in jail in 2012 for illegally acquiring credit and debit card details registered with PayPal.

JTRIG agents also sent messages that read "DDOS and hacking is illegal, please cease and desist" to Anonymous supporters via Facebook, Twitter, email, Skype and other instant messaging applications, NBC News reported, citing a slide that is not among those published.