More security holes are appearing in cryptocurrency and smart contract platforms

But the so-called 51% attack against Ethereum Classic was just the latest in a series of recent attacks on blockchains that have heightened the stakes for the nascent industry. A blockchain protocol is a set of rules that dictate how the computers in the network, called nodes, should verify new transactions and add them to the database. The only way to retrieve the money is, effectively, to rewrite history—to go back to the point on the blockchain before the attack happened, create a fork to a new blockchain, and have everyone on the network agree to use that one instead.

Source: www.technologyreview.com