I hope this isn’t an inside job or an exit scam. Unfortunately, situations like this are not new, so it's not really surprising anymore.
The other exchanges now have an idea of what they'd do if something like this happened to them. It's either they admit the real fault or incompetency that they have or some reasoning and point it to known groups. Well, these hacks do target exchanges that are quite big and any amount that's taken on them should be taken care of the management and yes, I do hope it's not an inside job.
Lesson learned here: aside from avoiding storing your coins in an exchange, it's also important to choose exchanges with a solid reputation and proven track record. For example, Binance, which was once hacked, still managed to stay operational thanks to their insurance (SAFU fund), even after losing a significant amount.
There are hacks that probably happened and only the exchange itself knew it and didn't want to broadcast if they were not big in damage. But I agree that always choose the exchange that's reputable and never store all of the funds that you have. In the case of Indodax, it's a known exchange in Indonesia cmiiw.