He wrote that while North Korean cyberattacks have been going on "largely unchecked" for about a decade, such activity has grown "more egregious" and WannaCry was "indiscriminately reckless".
Pyongyang has previously denied being responsible for the attack.
The Trump Administration is set to formally name North Korea as the power behind the WannaCry cyberattack that affected hundreds of thousands of computers in 150 countries over the summer.
Bossert said that the U.S. would "publicly attribute" WannaCry to North Korea, describing the attacks as "cowardly" and "careless". The malware targeted several hospitals in the United Kingdom, as well as banks and various other infrastructures and companies worldwide, causing malfunctions in critical sectors.
The attack exploited a Windows vulnerability that was originally developed by the US National Security Agency, but was released in a stolen cache of NSA cyberweapons by hacking group known as the Shadow Brokers. In an unusual twist, Hutchins was arrested months later by the Federal Bureau of Investigation during a visit to the US; he pleaded not guilty and now awaits trial on charges he created unrelated forms of malware.
Bossert closes out his article by stating that North Korea "continues to threaten America, Europe and the rest of the world - and not just with its nuclear aspirations".
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Mr Oh was shot and badly wounded by his fellow North Korean soldiers while fleeing across the border into the South last month.
But, the US government has assessed with a "very high level of confidence" that a hacking entity known as Lazarus Group, which works on behalf of the North Korean government, carried out the WannaCry attack, senior officials told Reuters.
The Lazarus Group is also thought to be behind the 2014 cyber attack against Sony, which resulted in the leak of several unreleased films.
Baik Tae-hyun, spokesman of South Korea's Unification Ministry, which deals with matters related to North Korea, said Monday that the Seoul government was examining whether the North was behind hacking attacks on a cryptocurrency exchange in June.
While North Korea is the main focus of Bossert's claims in the Op-Ed, he does not forget to talk about alleged 2016 election meddling by Russian hackers or the US's issues with Iran either.