The Japanese cryptocurrency exchange Coincheck was hit hard Friday.

A hacker managed to funnel out 500 million NEM coins, a value of more than $424 million USD, one of the exchange's co-founders said at a news conference in Tokyo Friday, according to Bloomberg. Japan’s Financial Services Agency is also investigating the theft.

Coincheck announced in an updating blog post that it had stopped trading of NEM and other coins as it dealt with the hack. Only Bitcoin services remained available on the exchange.

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The NEM coin tanked precipitously because of the theft, but it's already rebounding.

The hack is one of the biggest ever, almost matching the $500 million loss from the Mt. Gox exchange in 2014. When 850,000 bitcoin was taken from that Japanese exchange, it marked the end for the leading digital wallet and the company has since declared bankruptcy.

For Coincheck, it's now a matter of keeping other crypto-assets safe as they investigate what happened.