The US believes that the hackers who stole the $615m from the players of the game were from North Korea.
The game can be played through game play or trading.
The hack is likely to be the biggest ever.
US officials say that the breach was linked to a group called "Lazarus", which is believed to be controlled by North Korea's primary intelligence bureau.
The FBI said in a statement on Thursday that they had confirmed that the cyber actors associated with North Korea were responsible for the theft.
The Lazarus Group was accused of hacking into Sony Pictures and leaking confidential data.
The group demanded that Sony withdraw its film The Interview, a comedy about a plot to kill a North Korean leader.
The UN panel that monitors sanctions on North Korea has accused the country of using stolen funds to support its nuclear and missile programmes.
The United States is aware that the Democratic People's Republic of Korea has increasingly relied on illegal activities to generate revenue for its weapons of mass destruction and missile programs, as it tries to evade robust US and UN sanctions, according to a Treasury Department spokesman.
According to a 2020 US military report, North Korea has been hacking for at least the mid- 1990s and has grown to a 6,000-strong cyber warfare unit, known as Bureau 121, which operates from several countries.
One of the most successful years on record for cyber-criminals in the closed-off east Asian state was when North Korean hackers stole almost $400m worth of digital assets.