The Zencash network was hacked earlier today via a 51% attack. The hackers appear to have successfully reorganized the blockchain several times, double spending two transactions.
A 51% attack is a type of attack where a person or a party is able to gain control of 51% of the hash rate. This allowed the attacker to reorganize the blockchain, to the point the attacker was able to roll back 38 blocks. The attacker was also able to double spend two large transactions of 13000 and 6600 ZEN, currently worth about $550000. Mining pool operators notified the ZenCash dev team of the potential attack and exchanges were swiftly warned to increase confirmation times.
This is the fourth major 51% attack that has been launched within the past few months, with Bitcoin Gold and Verge having been hit as well. These types of attacks have sparked a raging debate in the crypto community as the ASIC vs GPU question remains to be answered.
Last week, a website was launched that showed the costs incurred in renting out enough hash power via NiceHash to make attacks on specific networks. In a shocking turn of events, several cryptocurrencies were not only cheap to attack but also had plenty of hash rate for sale on NiceHash. Older models of the 51% attack usually included the costs of hardware, electricity, and maintenance. This new method of attacking a network, dubbed “rent-a-attack”, is proving a danger for smaller crypto networks