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Remember when NFTs sold for millions of dollars? 95% of the digital collectibles are now probably worthless.
(markets.businessinsider.com)
This is a most excellent place for technology news and articles.
"bulletproof"
Blockchain can be hacked, just like any other digital technology. In fact, it has already happened.
If you write smart contracts with vulnerabilities, they'll be hacked, that is not the same thing as a blockchain being hacked though. Also, smart contracts can be fully audited and provably correct, a lot of companies just half ass it. ERC721 spec (NFT) has drop-in contract code which no doubt has been audited and not hacked on its own.