It was the second consecutive hack in the past two weeks.
After the announcement, a rumor spread that the server inspection was a result of an attempt by hackers to steal cryptocurrencies out of Bithumb's online wallets. As of press time on Wednesday, the Coinrail platform was still down for system maintenance.
"We remind you once again that there is no damage to you", Bithumb's update meanwhile reassures users - reiterating that lost funds would be reimbursed using some of its $450 million in company funds.
Twitter user RedDragon_ posted an email screenshot which reads, "We noticed that between last night and today early morning, about 35,000,000,000 KRW worth cryptocurrencies have been stolen". Whether this was somehow linked to the hack is unknown.
The exchange stated the amounts will be refunded, and it has removed all other assets to cold wallet storage.
Bithumb has announced that they are shifting their wallet system and its security protocols. However, the server check, which was to upgrade Bithumb's security protocols, exceeded the scheduled few hours.
The platform added that the stolen money will be covered by the exchange's reserves, and customer assets have been transferred to a cold wallet that stores cryptocurrencies in an offline environment that is not accessible via the internet.
The exchange, the sixth busiest in the world according to Coinmarketcap.com, said it had stored "all clients' assets in safe cold wallets", which operate on platforms not directly connected to the internet.
The incident marked the second time a South Korean exchange had been hacked this month.
Coinrail may be one of Korea's smaller exchanges, but Bithumb is far larger. However, the effect of the Bithumb hack has seemingly sent Bitcoin's value into a downward slide to just $6,562 in the last 24 hours. Thus, some experts declared that the hack was responsible for the decline.
The $30m Bithumb hack announced on Twitter on June 20, 2018, affected the cryptocurrency markets, but prices held reasonably firm. Still, the frequency of cryptocurrency exchange hacks is something that will leave many traders anxious. It said it would "make up" all losses.
Bitcoin (virtual currency) coins placed on Dollar banknotes are seen in this illustration picture, November 6, 2017.