Hackers have stolen roughly 58 billion yen ($532.60 million) from Tokyo-based cryptocurrency exchange Coincheck, raising questions about security and regulatory protection in the emerging market of digital assets.

The following are some questions and answers about one of the largest heists of cryptocurrencies in the history:

What Is NEM?

NEM is a cryptocurrency launched in March 2015 by a team of five developers identifying themselves as Pat, Makoto, Gimre, BloodyRookie and Jaguar. Its acronym stands for New Economy Movement and, like other cryptocurrencies, markets itself as a digital coin outside the control of governments and central banks, which can be used for fast, global transactions.

It is now the tenth largest cryptocurrency, with $9 billion worth of NEMs in circulation, trading at just below $1 per coin.

NEM was launched to rectify the high concentration of wealth that some in the cryptocurrency community believe to be one of the key weaknesses of bitcoin, the world’s most widely known cryptocurrency, whose early adopters have turned into multi-billionaires.

Read: Starbucks Chairman Schultz Rambles About Bitcoin on Earnings Call

For bitcoin transactions to clear, computers compete to find the solution to a computational problem, which NEM developers say makes the rich richer as those who have money can afford more hardware to solve such problems.

NEM rewards accounts that participate in the economy. The balance of an account, who transacts with that account, and how much it transacts with others are all combined to calculate an account’s importance, based on which transactions are cleared.

How Was Coincheck Hacked?

Many details are still unclear.

Yusuke Otsuka, Coincheck’s chief operating officer, said on Friday that around 523 million NEM coins were sent from a NEM address at Coincheck at around 3 a.m. local time. Over eight hours later, Coincheck noticed an abnormal decrease in the balance.

Coincheck said the NEM coins were stored in a “hot wallet” instead of a “cold wallet.” Company President Koichiro Wada cited technical difficulties and a shortage of staff.

What Is a Hot Wallet

Hot wallets are connected to the internet, therefore vulnerable to hacking. Experts warn that holding large sums in hot wallets is the equivalent of carrying large amounts of cash in person.

Cold wallets, such as Trezor and Ledger Nano S, are devices which can be as small as a USB stick and can be stored offline. Some keep them in a safe.

How Are Crypto Exchanges Regulated in Japan?

Japan’s government in April recognized bitcoin as a legally accepted means of payment, and required exchange operators to register with the financial regulator.