Wow, this is really horrible. And I thought Nicehash were unshakable. I really pray thus is a rumor, cause a lot of people would surely be affected.
I would advice you use only a credible bitcoin mining site like Genesis mining. There also others like Hashflare, VIABTC, Hashnest.
But, yet even with these, make sure to mime with extreme caution.
RE: NiceHash possibly Hacked, 4000+ BTC gone.