The exchange encouraged community members to block deposits from the offending wallet, but didn’t have leads to identify the owner. There’s a wide range of potential candidates. It could be typical online criminal organizations, an inside job, or nation states hoping to pad their funds when sanctions leave them cash-strapped.
This isn’t the largest crypto theft to date. Coincheck lost $400 million in NEM tokens to a hack at the start of 2018, for instance. However, it’s still doing significant damage. It also suggests that exchanges may need to do more to lock down transfers to prevent large-scale theft like this.