Instead, Flashpoint said, it was "moderately confident" that the Hackforums community was behind the attack which led to well-known sites like Twitter, Spotify, Netflix and Paypal being inaccessible on 21 October (US time).
The Hackforums community is an English-speaking one and it was here that the source code for the Mirai malware, that can be used to attack Internet-of-Things devices and take them over for use in a botnet, was released by someone using the pseudonym Anna-Senpai.
Clapper was quoted in The Hill as saying: "That appears to be preliminarily the case. But I wouldn’t want to be conclusively definitive about that, specifically whether a nation state may have been behind that or not."
His claim must be assessed in the light of an earlier 2013 statement that the NSA was collecting any type of data on millions of Americans. It was found to be untrue following the revelations by NSA whistleblower Edward Snowden that precisely the opposite was the case.
Flashpoint director of security research Allison Nixon said that the infrastructure used in the attack had also targeted a well-known video game company.
"While there does not appear to have been any disruption of service, the targeting of a video game company is less indicative of hacktivists, state-actors, or social justice communities, and aligns more with the hackers that frequent online hacking forums," she said.
"These hackers exist in their own tier, sometimes called 'script kiddies', and are separate and distinct from hacktivists, organised crime, state-actors, and terrorist groups. They can be motivated by financial gain, but just as often will execute attacks such as these to show off, or to cause disruption and chaos for sport."
Nixon wrote that Flashpoint assessed with moderate confidence that the most recent Mirai attacks were "likely connected to the English-language hacking forum community, specifically users and readers of the forum 'hackforums[.]net'.
"The personalities involved in these community are known for creating and using commercial DDoS tools called 'booters' or 'stressers'. The hackers offer these services online for pay, essentially operating a 'DDoS-for-hire' service.
"One of the few known personalities that have been associated with Mirai malware and botnets is known to frequent these forums. A hacker operating under the handle 'Anna-Senpai' released the source code for Mirai in early October, and is believed to have operated the original Mirai botnet that was used in the attack against Krebs on Security and hosting provider OVH. The hackers that frequent this forum have been previously known to launch these types of attacks, though at a much smaller scale."
Nixon said the technical and social indicators of the attack aligned more closely with attacks from the Hackforums community.
"These other types of threat actors are unlikely to launch such an attack without a clear financial, political, or strategic objective, and they are very unlikely to launch an attack against a video game company," she pointed out.
"Participants in the Hackforums community have been known to launch DDoS attacks against video game companies to show off their credentials as hackers of skill, or to 'troll' and gain attention by causing disruption to popular services."