In today's Bitcoin in Brief – Zencash has lost $550,000 in two double-spend transactions following a 51% attack on the network. Developers have taken measures to increase the difficulty of future attacks. The event-ticketing platform Ticketfly is also trying to recover from a hijack. 26 million accounts have been reportedly compromised by a hacker who asked for bitcoin ransom.

Zencash Attacked with Two Double-Spends

The Zencash network has been targeted in a 51% attack on Saturday, June 2. The attacker managed to successfully perform two double-spend transactions while reorganizing the blockchain multiple times and reverting 38 blocks in the longest reorganization.

According to a released statement, the Zencash team received warning of potential attack from a pool operator and took measures to raise the difficulty of future attacks on the network, contacting exchanges to increase confirmation times and recommending a minimum of 100 required confirmations.

The attacker(s) caused the reorganizations of the blockchain between blocks 318165 and 318275. They performed the double-spend attacks in blocks 318204 and 318234 – for 13,000 and 6,600 ZEN, respectively, worth more than $550,000 at current prices.

According to the forensic analysis conducted with the affected exchange, the suspect pool address is znkMXdwwxvPp9jNoSjukAbBHjCShQ8ZaLib and the suspect exchange deposit address is zneDDN3aNebJUnAJ9DoQFys7ZuCKBNRQ115.

At the time of the attack the network's hashrate was 58MSol/s. Developers believe that the attacker has a private mining operation large enough to conduct the attack and/or supplement with rental hash power. Zencash is a proof of work coin based on the equihash algorithm. All equihash-based networks are exposed to possible influx of new equihash power, the team noted.