According to the post released by Ethereum Classic Consortium on its official Weibo account, the security team SlowMist has detected transaction rollbacks happened to many blocks and sent out an alert. The ETC community followed up on the development of the incident immediately and learned that there is a private mining pool (address: 0x3ccC8F7415e09BEAd930dc2B23617bD39ceD2C06) that achieves more than 50% of the total network hashrate at certain times.
The post also said, "Our member Roy has been closely monitoring the development of the incident with other developers in the team. So far, the ETC network has not been substantially affected, and we are temporarily unclear about the purpose of the perpetrator. In order to prevent potential attacks, we call on exchanges and mine pools to increase the time for deposit and withdraw (+400) until the alert is lifted.
SlowMist reposted the post and commented: "We're trying to trace the cause and will announce it as soon as we get the results."
CoinNess.com earlier reported that SlowMist sent out an alert that the Ethereum Classic (ETC) network might have been targeted by a 51% attack, and that many blocks were underway transaction rollbacks.