The incident allowed the attackers to spend the same virtual coin twice
Anybody can’t spend the same cryptocurrency for two different transactions. For example, each transaction made with Bitcoin is registered in a database (named blockchain) to which anyone can access to ensure that there is no fraud; or at least that’s what we thought.
According to cybersecurity and ethical hacking experts from the International Institute of Cyber Security, the cryptocurrency trade platform Coinbase reported that transactions with Ethereum Classic asset would no longer be supported on its platform, as the stock exchange found that Ethereum had been the victim of a cyberattack that allowed a user to spend the same coin twice.
According to reports, this attack was presented thanks to a problem known to the developers of blockchain since the emergence of these virtual assets. The cryptocurrencies are only safe while users are honest in maintaining the blockchain that registers the transactions. Coinbase cybersecurity expert Mark Nesbitt mentioned that this attack (known as the 51% attack) was presented because the attackers took control over the half the processing power of the computers that store the blockchain of Ethereum Classic. This allowed the attackers to create alternative transactions of some currencies, in other words, to spend twice the same coin.
Through Twitter, Ethereum mentioned that they had detected a problem, but did not contemplate that it was a 51% attack nor had evidence to indicate that some currency had been spent twice by the same user. “Coinbase allegedly detected an attack, but did not contact the Ethereum Classic team,” they mentioned.
According to reports of experts on cybersecurity, the currencies that allegedly would have been spent twice were worth about $460k USD. Coinbase believe that the potential to deploy this type of attack is inherent to any cryptocurrency blockchain, so they rule out that Ethereum Classic or any other virtual asset is especially vulnerable to a 51% attack.