The Japanese cryptocurrency exchange, Coincheck had 523 million XEM coins stolen by hackers Friday amounting to around 58 billion yen or $534.8 million USD. According to Coincheck the coins were stored in a hotwallet that was connected to the internet instead of cold storage (stored offline). Although Coincheck's website indicates that it uses cold storage, it does not say what percentage of the assets are offline. The American exchange, Coinbase, stores 98% of it's digital currency in cold storage to protect assets from hacking.Recently a South Korean cryptocurrency exchange named Youbit lost 17% of its digital assets. Its parent company Yapian filed for bankruptcy.
The security page on Coinchecks website states, "Coincheck asks users to enable SMS and two-factor authentication with authentication apps provided by Google (Google Authenticator / iOS, Android). We manage cold wallet on redundant and distributed servers. Therefore, your assets will be protected safely even if our system partially damaged due to disasters such as a fire hazard."
Coincheck Interview: http://logmi.jp/260622