Coincheck is a Tokyo based cryptocurrency exchange, which primarily serves the people of Japan. Their CEO confirmed that their systems were hacked, and an estimated 58-billion-yen worth of crypto was taken, which translates to $533 million. This was in the form of about 500 million XEM token, which is the currency for the NEM cryptocurrency.
The price of XEM dropped from about $1.01 down to $.85 after the announcement, thought whether that is directly related to the hack or not is not clear.
Assuming all the numbers remain about the same, this will mark the largest hack in crypto history, and almost certainly one of the costliest hacks overall. The most famous hack was to Mt. Gox , where about $340 million in Bitcoin were stolen. At the time, this was a much larger percentage of the overall crypto market cap so it had a huge impact. This hack, while significantly larger in total amount, is very small in comparison to the entire crypto economy.
Likely the most important impact of this is that it will serve as yet another reminder that those in the crypto world need to keep their money off of exchanges unless they are actively trading with it. No exchange is entirely secure, and it is the responsibility of holders to get their coins and tokens to a secure storage system as quickly as possible.