Thomas Bossert, counterterrorism adviser to President Trump, said the USA has evidence that "cyber affiliates of the North Korean government" were involved in the attack.
"We support the actions of our cyber security partners in calling out this sort of reckless and malicious cyber activity".
Those who remember May's attack, which locked down the systems of hospitals, banks, and other companies across the U.S., might recall Marcus Hutchins-a 22-year-old hacker known as MalwareTech-was credited with stopping the spread of WannaCry.
North Korea was widely suspected to have created the virus, which was paired with ransomware that encrypted data on victims' computers and demanded a ransom to restore access.
"The GCSB has two main functions, collecting intelligence in accordance with the Government's priorities and providing cyber security and information assurance services to organisations of national significance, from both the public and private sector".
In the piece titled "It's Official: North Korea is Behind WannaCry", Bossert characterized the attack as "cowardly, costly and careless".
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"Cyber threats continue to increase, in part because of New Zealand's global connectivity but also because the cost barriers are low, and getting lower, while the potential for harm is vast". "Our adversaries are not distinguishing between public and private so neither should we. government and industry must work together, now more than ever, if we are serious about improving our collective defense".
The National Security Agency linked North Korea to the worm's creation in June.
In retaliation for the cyberattack, President Donald Trump plans to summon "all responsible states" to unite against North Korea and push for new United Nations Security Council sanctions, according to The Hill. "It gives them something else to bring to the table".
North Korean leader Kim Jong Un. Until now, the US government has not publicly stated as much.
CNN reported in June that United Kingdom intelligence believed a group associated with the North Korean government was behind the attack, and The Washington Post reported around the same time that the National Security Agency had reached a similar conclusion.
North Korea has grown increasingly adept at breaking into computer systems around the world for financial gain and strategic benefit.
The hackers drew worldwide headlines in 2014 when they allegedly broke into Sony Corp.'s movie business as it was preparing to release "The Interview", a Seth Rogen and James Franco comedy about meeting the North Korean leader.