FBI Director James Comey said at the International Conference on Cyber Security North Korea got sloppy with its proxies and revealed themselves in the Sony hack. Comey said he d like to quell the critics by telling the whole story of why the FBI claims it came to know North Korea was behind the attack. He also acknowledged the importance of keeping secret the FBI s valued investigatory and forensic techniques regarding how they see what they see Comey: There is not much in this life that I have high confidence about this attribution as does the entire intelligence community””,January 8
Source: https://threatpost.com/fbi-director-attribution-detractors-dont-have-all-the-facts/110277/