maybe yes maybe no,
it's already showed in their website that their security has been breached.
go look it here :
https://www.nicehash.com/their services at this moment unavailiable because of security issue and will only stopping their service for 24 hours.
not really sure about hacked or not but all that we understand at this moment is their website currently offline.
if they can open up their website again in the next 24 hours just like what they said,
i think it would be best for you to withdraw your money as soon as possible from those exchange.
not recommend doing anything in there if they're opening it again in the future.