ZenCash 51% Attack. $550.000 Stolen

ZenCash 51% Attack. $550.000 stolen in double spend transactions

On June 2, ZenCash’s blockchain suffered from a “51% attack”, as a result of which unknown hackers stole more than $ 550,000 in the equivalent of ZEN cryptocurrency. The initiator of the attack, which captured more than 51% of the hashpower in proof of work blockchain, was able to reorganize the blocks in the blockchain and re-use two large transactions.

Hackers double spent two transactions for 13,000 ZEN and 6,600 ZEN. According to representatives of ZenCash, the funds were withdrawn to the following address: zneDDN3aNebJUnAJ9DoQFys7ZuCKBNRQ115.

The ZenCash 51% attack took place on 2 June at about 2.45 am UTC.

ZenCash Team made announcement in its blog on Sunday morning:
“The ZenCash network was the target of a 51% attack on 2 June at approximately 10:43 pm EDT. The ZenCash team immediately executed mitigation procedures to significantly increase the difficulty of future attacks on the network.”

The attackers managed to reorganize over 100 blocks, and the attack itself lasted less than four hours. The largest modified chain contained 38 blocks. The attacker was able to re-use two large transactions for a total of $ 550,000. ZenCash 51% attack cost the hackers $30,000. Mining-pool operators informed ZenCash team about potential network problems. ZenCash team recommended all cryptocurrency exchanges to increase the number of transaction confirmations for deposits.

Previous 51% Attacks

Thus, ZEN has become the fourth cryptocurrency for the last few months, which has been suffered from 51% attack. Earlier Bitcoin Gold and Verge became a victim of 51% attack.


The ZenCash team has recommended users to store funds in a hardware wallet like the Ledger Nano S.
“Increasing required confirmations to 100 makes another attack highly unlikely, however, if you have any specific concerns about the general security of exchange platforms, please contact the exchange directly. As always, we recommend that users store their funds in wallets that they control such as cold storage with something like a Ledger Nano S or paper wallet.”

About ZenCash

ZenCash is a cryptocurrency with the mechanism of consensus Proof-of-Work and the Equihash algorithm of mining. Equihash is used in several other large cryptocurrencies. ZenCash is the fork of ZClassic, which was launched in May 2017 using the ZCash code.

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