Coinrail, a South Korean cryptocurrency exchange, became latest to close down after hacking attack.

The Korean virtual currency exchange announced on Monday that it has shut down its system for maintenance after detecting a hacking incident Sunday. It said about 30 percent of its cyber assets were stolen by hackers, but did not disclose the lost value. Market experts estimate the loss of 30 percent would have cost Coinrail around 40 billion won ($37 million).

Coinrail said on its website that it so far has worked with other exchanges to freeze or recall about two-thirds of its exposed coins including Pundi X (NPXS), NPER, and Aston (ATX). The remaining one-third of the affected coins is under probe by investigating authorities, relevant exchanges, and coin developers, it added. The exchange has also completed moving 70 percent of its cyber assets to a cold wallet, a computer system that is not connected to the Internet, to protect virtual currency from theft.

The latest hacking in the Korean cryptocurrency exchange is smaller than those of other previous cyber attacks in value, including the nearly $500 million theft from Japanese exchange Coincheck Inc. in late January. Still, it has spooked investors with concerns that it would happen to other crypto exchanges. The latest hacking incident would further weaken demand for cryptocurrencies amid lingering concerns over the security of the crypto exchanges due to lack of regulations, industry experts said.

Coinrail is a mid-sized cyrotocurrency exchange ranking about 90th in the world based on 24-hour trade volume. It is not a member of Korea Blockchain Association, which leads self-regulation among cyrotocurrency exchanges in the country.

Prior to this incident, two other Korean cyrptocurrency exchanges Yapizon and Youbit had lost virtual coins worth 5.5 billion won and 17.2 billion won, respectively, due to cyber thefts.

By Oh Chan-jong and Cho Jeehyun

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