The biggest ever theft of digital currency is reported to have happened in Japan with roughly £380m ($534m) stolen by hackers.
Coincheck has suspended deposits and withdrawals for all crypto-currencies except Bitcoin as it assessed the losses in NEM, the 10th-largest digital money by market value.
If the theft is confirmed, it will be the largest involving online-only currency and it has already had ripple effects on other currencies.
Another Tokyo exchange, MtGox, collapsed in 2014 after admitting that $400m (£282m) had been stolen from its network.
The stolen Coincheck money is thought to have been kept in a “hot wallet” in the internet - as opposed to a cold wallet where funds are stored offline. A hot wallet is a way of keeping the money online and connected, in some way, to the internet.
Coincheck says it has the digital address of where the money was sent and says it is going to do what it can to compensate investors.
Shortly before 3am in Japanese time hackers broke in with the breach not discovered nearly eight and half hours later.
Company CCO Yusuku Otsuka said 523m NEMs had been stolen during the breach.
At a press conference at the Tokyo Stock Exchange he said: "It's worth 58bn yen based on the calculation at the rate when detected.
"We know where the funds were sent.
"We are tracing them and if we're able to continue tracking, it may be possible to recover them.
"But it is something we are investigating at the moment."
Otsuka said Coincheck is considering compensating clients if it cannot recover the tokens, reports the Japan Times but he declined to say whether Coincheck had enough cash to do so.
Coincheck does not know exactly how many customers have been affected or from what country the hack was launched.
The value of NEM fell 11% over a 24-hour period to 87 cents, reports Bloomberg News. Bitcoin also dropped 3.4% and Ripple 9.9%.
Japanese police are investigating.