Hotbit is famous for faking volumes on there exchange so I doubt that they had indeed 2M user registered on there exchange.
Registered users!That doesn't mean users with a balance and users that actively trade there.
And even if we would consider those even a guy trading 5 satoshi worth of shitcoins once a year would still be a user.
Hotbit is a destination for last resort dumping of coins that aren't traded anywhere else and usually, the ones doing that instantly convert to a more serious coin and withdraw it immediately, so the number of actual coins held in cold storage by them could be disproportionately lower than other exchange who claim the same volumes.
Simply because this criminals can sell this underground, KYC's and all of the stuff and they can used all those accounts to send email with crypto phishing. Win win for them. So stay tune, we might here in the next two weeks of crypto users getting lots of phishing email from this breach.
Email phishing would be the last concern of users that have gone through all those checks.
If they had the level of access to allow them to delete a database it's highly probably they've got control over all the servers and not just lines in the DB actually KYC submitted files. Those exchanges are usually so lazy or spend so little in securing those not even mentioning using a 3rd party as they can't afford one so it shouldn't surprise anyone if their documents are now used to open accounts on god knows what website right now.
And don't forget, they have your balance and your real-life address, for someone in the US and Europe might bot be a problem but in other countries with no laws and insane crime rate that might be something really concerning