What just happened? For the second time this month, a South Korean cryptocurrency exchange has been hacked and suffered millions of dollars’ worth of losses. This time, it was popular Seoul-based Bithumb that was the victim, with 35 billion won ($31.5 million) stolen from the platform.

Unlike Coinrail, which lost more than $40 million in altcoins when it suffered an attack, Bithumb is one of the biggest exchanges—according to CoinMarketCap data, it's the world’s sixth largest cryptocurrency exchange.

The hack began at around 11 pm local time yesterday and lasted until this morning. Bithumb has suspended all withdrawals and has asked customers not to deposit any more funds until further notice. Much like Coincheck did after suffering an attack at the start of the year, Bithumb has promised to compensate all losses.

Last week, Bithumb tweeted that a database and security upgrade was being carried out, and that part of the process involved transferring assets to a cold wallet (one not directly connected to the internet). Whether this was somehow linked to the hack is unknown.

As was the case with Coinrail attack, the price of Bitcoin, Ethereum, and Ripple all fell on the back of the news but have since recovered.

Two massive attacks within two weeks on separate Korean exchanges have raised concerns. The Korea Internet & Security Agency said it is now investigating the matter, and Seoul police have been sent to Bithumb's HQ to collect records and data from its computers.