Two men have been arrested in Tokyo for obtaining cryptocurrency linked to the massive hack of Japan's Coincheck exchange in 2018.

As reported by Jiji Press Wednesday, the men were held by the Metropolitan Police Department for allegedly obtaining NEM that were the suspected proceeds of crime – illegal under the law relating to punishment of organized crime. One of the two arrested – who are claimed to have known the tokens were stolen – is a doctor from Hokkaido and the other is a company exec from Osaka.

Coincheck suffered possibly the biggest-ever breach of a cryptocurrency exchange in January 2018, losing around $530 million worth of NEM. The hack was likely bigger even than that of Mt. Gox, which is thought to have lost $340 million in bitcoin over a period of time.

Tokyo police believe the arrested individuals have been exchanging the NEM for other crypto assets since February, Jiji said.

The arrests are the first relating to the Coincheck hack and come after Tokyo police formed a task force to investigate the theft.

Coincheck was taken over by online brokerage Monex Group later in 2018 and was approved for an operating license in 2019, after making improvements to its systems.