Enlarge / It’s where the money is. (credit: iStock/Getty Images)

The Japanese cryptocurrency exchange Coincheck has shut down trading and withdrawals from accounts after a reported theft of more than 500 million XEM—the blockchain-based cryptocurrency created by the NEM Foundation. At the time of the theft, 500 million XEM was worth approximately $ 400 million US. Police were reportedly at Coincheck’s offices.

Coincheck announced the shutdown of NEM deposits at about noon Japan Standard Time Friday (10:00pm Eastern Time on Thursday). In a follow-up announcement four hours later, a company spokesperson expanded the shutdown to all currencies, and by 6pm JST all payment processing had been suspended. “We sincerely apologize for these inconveniences and will continue to do our best to be back to normal operations as soon as possible,” the spokesperson wrote. At about the same time, police were seen at Coincheck’s offices.

さっき事務所にいったら、
コインチェックさんの前にパトカーが、、！！#リップラー八木 #仮想通貨 pic.twitter.com/91zJxpiy8e

— ぷちぱ☆ 八木ひなた 3.21ワンマン (@yagihinata) January 26, 2018

Ars attempted to reach representatives of Coincheck and the NEM Foundation without success. Lon Wong, the president of the NEM Foundation, was quoted by Sead Fadilpašić and Stuart Garlick of Cryptonews.com as saying, “This is the biggest theft in the history of the world.” Wong told Cryptonews that NEM’s technology was not responsible and that Coincheck did not implement NEM’s multi-signature smart contract, “and that’s why they could have been hacked. They were very relaxed with their security measures.” It is not clear if there was actually a “hack” at this point.