One of Japan's biggest cryptocurrency exchanges said that about US$400 million ($543.8m) in NEM tokens were lost after the coins were sent "illicitly" outside the venue, spooking investors in a country that's still wary of digital-token exchanges four years after the collapse of Mt. Gox.
After hours of speculation, Coincheck Inc. co-founder Yusuke Otsuka said during a late-night press conference at the Tokyo Stock Exchange that the company didn't know how the 500 million tokens went missing, but the firm is working to ensure the safety of all client assets.
Coincheck said earlier it had suspended all withdrawals, halted trading in all tokens except bitcoin, and stopped deposits into NEM coins.
"We are looking into the facts surrounding Coincheck," Japan's Financial Services Agency said in a statement. The disappearance likely ranks among the biggest losses or thefts of investor assets since the advent of digital currencies with the launch of Bitcoin in 2009.
NEM, the 10th-largest cryptocurrency by market value, fell 7.5 per cent to 86 cents as of 11:28 a.m. New York time, according to Coinmarketcap.com. Bitcoin was down less than 1 per cent and Ripple retreated 5 per cent, according to prices available on Bloomberg.