bitcoin & blockchain technology is unhackable how come hackers stole 70 million worth of bitcoins from "NiceHash"
You are conflating two things. If Bitcoin cryptography were hacked, then it would be game over for that particular cryptocurrency (and for SHA-256). It would mean that someone figured out how to “print” a counterfeit Bitcoin.
What you refer to is the hacking of a website’s (web wallet) protocol for withdrawing bitcoin. That website did not have sufficient safeguards to protect depositors. This is prevented, these days, by requiring 2FA (various authenticators), holding BTC in cold storage (offline wallet) and email verification of withdraw.
Unhackable I think only means hackers can't create new bitcoins out of the blue or double spend. BUT: stealing seems easy. Viruses install keyloggers, get your passwords as soon they see your checking crypto-relevant sites. Using crypto on your normal Windows machine or cellphone is an invitation to hackers, McAffee says.
Burn yourself a linux live CD like Knoppix and use crypto only with this. So you always have a clean operating system when dealing with your private key.
Si se cree porque los estafadores se valen de cualquier cosa para lograr su cometido.