It was hardly a week back when Bitcoin gold succumbed to the malicious double spend attack when a miner gained 51 percent control of the network, making it the third altcoin to suffer losses from such kind of attack after Monacoin and Verge.
Becoming the latest victim of the attack is ZenCash (ZEN), a platform designed for secure communications and private economic activity, saw its network suffer a 51% attack on June 2 at approximately 10.43 pm EDT. The attacker managed to reorganize 38 blocks and make two double-spends, of 6,600 and 13,000 ZEN resulting in a loss of about $550,000 worth Zen crypto tokens.
It was possible for the attacker to roll back transactions, but it is unclear what he did with the initial transactions. If he sent them to an exchange and traded the coins for Bitcoin or some other cryptocurrency, the attacker made out like a bandit. The attack occurred over a span of around 110 blocks, making the total attack length under four hours.
The team became aware of the attack when a pool operator sent an alert message to them. The team immediately evaluated hash power distribution. At the same time, all exchanges which have listed ZenCash were advised to increase confirmation times. The investigation revealed that the suspected operation was a double spend. ZenCash team is conducting additional investigation with the affected exchange.
Regarding the 51% attack, ZenCash team has stated
“a 51% attack or double spend is a major risk for all distributed, public blockchains. All Equihash-based networks are exposed to an influx of new Equihash power and therefore the best short-term mitigation strategy is to recommend that all exchanges increase their minimum required confirmations to at least 100.”
When the attack was carried out Zen network hash rate was 58 MSol/s (Sol/s in Zcash is exactly the same as measuring TH/s in Bitcoin). ZenCash team believes the attacker has a private mining network big enough to conduct such an attack or have access to rental hash power. As the net hash rate is derived from the last mined block, live hash rate statistics are not available.
In theory, a 51% attack greatly undermines trust in the network. However, some assets have managed to survive, and this type of attack has become a general threat to the sector. After the news, the market price of ZEN fell by 4.78% to $28.48, but has kept most of its positions. ZEN trading volumes are slim. More than 64% of ZEN volumes are concentrated on Binance, but smaller exchanges may be more vulnerable.