UNITED NEWS INTERNATIONAL (UNI) — The largest South Korean bitcoin exchange is hacked overnight.

Bithumb posted on its website on Wednesday, June 20 it had stopped all trading after confirming more than $30 million worth of crypto-coins were stolen.

Hackers targeted the company on Tuesday night and Wednesday morning.

The virtual currency exchange has more than 1 million customers.

Reuters said the incident highlights the security risks of global cryptocurrency markets.

Bithumb, meanwhile, says the loss will be compensated by its own reservoir and all customers’ assets are ”securely saved in Bithumb’s cold wallet,”’

Ten days ago, hackers targeted another South Korean bitcoin exchange, Coinrail and stole $40 million worth of virtual coins.

Yonhap News says blockchain based crypto-coins are supposed to be difficult to steal because transaction details allegedly cannot be faked.

However, if the security of the exchange is weak it can be vulnerable to hackers.