Zencash is Hit with a 51% attack
Today Zencash was where $550,000 was doublespent at exchanges and the blockchain was rolled back 38 blocks. At the time of the attack the Zen network hash rate was 58MSol/s. So the attacker needed a large operation to pull off the attack.
Based on the website crypto51 the attack on ZEN could be as little as $30,000 to attack the zencash network.
At the time of the attack the Zen network hash rate was 58MSol/s. It is possible that the attacker has a private mining operation large enough to conduct the attack and/or supplement with rental hash power. Net hash rate is derived from the last mined block and therefore live hash rate statistics are not available.
The suspect pool address is
znkMXdwwxvPp9jNoSjukAbBHjCShQ8ZaLib. Between blocks 318165 and 318275, the attacker(s) caused multiple reorganizations of the blockchain, reverting 38 blocks in the longest reorganization. In block 318204 and 318234 the attacker(s) performed double-spend attacks-from Zencash blog Link
Post from WhaleReports Issue 7 About 51% attacks and BitcoinGold
A few days ago, $18 Million was stolen from exchanges by a Hacker performing a double spend attack. The hacker gained enough hash power to perform a 51% attack on the network and double spend. The attack was the third in the last few weeks on major cryptocurrencies, the others being Verge and Monacoin.
What is a 51% attack & double spending?
“Miners harnessing more than 50% of network hashing power can take advantage of this situation by sending funds to one address on the main chain, while sending the same funds to another address on a forked copy of the blockchain that is silently being mined with more hashing power than the main chain. Since other nodes only know about the main chain, they will see the first transaction as valid, and exchanges, etc will accept this transaction as valid. This malicious node can later release these silently mined blocks, and other nodes will accept this as the new 'correct chain' since it is longer. This will cause the original transaction to effectively disappear, and nodes will recognize the funds as being sent to the address from the new chain instead. This is known as a 'double spend' attack.”-source www.crypto51.app
How is this Happening?
There are people who either own enough mining equipment, or have the ability to rent the equipment from somewhere like NiceHash to overpower more that 51% of a network. An example of the attack would be depositing the coin being attacked into an exchange, trading that coin to another, and withdrawing. Then revert those blocks. A site recently popped up showing the cost to perform an attack like this called crypto51.app. Quite a few networks could be attacked for under $1,000 by renting space on NiceHash.
Some Positives
Performing a 51% attack can be a lot of work, time, and money to pull off successfully. If you control 51% of the network, you may make more from just mining than being malicious. Larger network coins like Bitcoin and Ethereum would be very costly to attack. Moving forward, new coins and networks will need to be aware and work on protecting themselves against attacks like this.
Coins mentioned in post: