MIT Technology Review has the article Once hailed as unhackable, blockchains are now getting hacked.
More and more security holes are appearing in cryptocurrency and smart contract platforms, and some are fundamental to the way they were built.
It had to happen. It is almost an irrefutable principle that anything designed by humans to be secure, can be broken into by some other devious human.
See the previous post The Lunacy of Cryptocurrency for comments on the economic reasons why cryptocurrencies have problems.