I have never used them, but I hoped they could give more information on how the hack occurred without any private key breach. I also understand that giving detailed information can serve as a blue print for other scammers and make them a target.
According to this
article published today, BigOne exchanger said that the attack path had been identified and contained, and that no further losses are expected. There is no further details. Maybe because it's still under investigations by legal authorities.
The insident occured three days ago and this is what confirms that this exchange is not that popular because this explains how none here in bitcointalk notice and post about it until day 3, which confirms a big loss even the amount is not that big compared to other hacks from the last two years.