Over the weekend ZenCash (ZEN) was the target of a 51% attack that cost them half a million dollars in double-spent tokens.
The Proof of Work (PoW) cryptocurrency is a fork of ZClassic, which uses the same codebase as ZCash. They both run on the very popular and widely used Equihash mining algorithm, meaning there is a large amount of available hash rate that can be used against any other Equihash network.
During the 51% attack, the hacker was able to rollback 38 blocks. This type of blockchain reorganization allowed him to double spend two huge transactions worth almost 20,000 ZEN combined. At the current ZEN exchange rate, that comes to more than 550,000 US dollars.
ZenCash were quickly notified of the potential attack and warned exchanges to increase confirmation times.
The attack lasted around four hours and covered 110 blocks, which, according to popular new estimate website Crypto51, would have cost the attacker approximately $30,000. It’s unsure if the attacker has converted to transactions to Bitcoin or some other cryptocurrency yet.
Since the launch of Crypto51 the reality of how easy some networks are to attack has become apparent. Previously it required lots of expensive equipment, but now the ability to rent hash power on NiceHash has vastly reduced the cost of such attacks and made them easier to instigate.
Bitcoin Gold (BTG) and Verge (XVG) were the most recent victims of similar attacks.
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