SEOUL, South Korea (AP) — A leading South Korean cryptocurrency exchange said Wednesday that $31 million worth of virtual currencies have been stolen by hackers, a latest in the series of recent hacks that raised security concerns.

Bithumb, South Korea's second-largest exchange, said cyberattacks from late Tuesday night to Wednesday morning led to the loss of 35 billion won worth of cryptocurrencies.

Bithumb said it has suspended trading and exchanging cryptocurrencies to Korean won following the hacking.

It did not say which types of coins were lost. The company promised it would compensate the loss.

It is the latest series of cyberattacks on crypto exchanges that have raised security concerns for investors. Earlier this month, a small exchange in South Korea called Coinrail was hacked and reportedly lost coins worth $37 million.

Beefing up security on crypto exchanges will be a key in shoring up confidence in the largely unregulated sector that has risen as one of the hottest investment areas.