Coincheck have said that $523 million of a Japanese exchange’s NEM coins were sent to another account at around 3am local time.
After the hackers stole the cryptocurrency, Coincheck then restricted withdrawals of all currencies including yen and trading of cryptocurrencies other than bitcoin.
Coincheck management said it held the coins in a “hot” wallet, which is a method of storage linked to the internet.
This is the reason why you should never park your coins in an online crypto exchange.