Coindesk has reported that Coinbase has suspended all Ethereum Classic transactions, withdrawals and deposits due to a series of blockchain history reorganisations on the network.
ETH Classic has seen more than 100 blocks reorganised during a 51 percent attack on Sunday, 6th January, and Coinbase wrote in its blog post that it had detected some 88,500 ETC being double spent, totalling some $460,000.
Coinness also reported on Monday 7th January that one of its in-house analysts had detected an abnormal hash rate going into a single mining pool, potentially causing mass reorganisations of mined blocks. Although the people behind ETC refuted this at first, a later tweet appeared to confirm that there were some problems. It said, “We are now working with Slow Mist and many others in the crypto community. We recommend exchanges and pool significantly increase confirmation times.”
SlowMist is a security firm based in China and it alerted users to strange activity on the network on Monday morning, saying that it was trying to trace the source of the attack. How long the attack lasted for is being disputed: Blockscout reported block reorganizations occurring at 02:00 UTC and 05:00 UTC Monday, while Bitfly tweeted at 17:00 UTC that the attack was potentially “ongoing. Coinbases concurs with Bitfly’s assessment of the situation.
Cody Burns. An ETC development advisor, told Coindesk that the activity could not be labelled a 51 percent attack but rather “a selfish mining attack” caused by a client-local phenomenon. He also tweeted the following message: “…the entire Ethereum network doesn’t ‘reorganize’ simultaneously. It would be more likely that someone discovered all of Coinbase ETC nodes and ‘surrounded’ them.”
Other exchanges have also responded to the situation, with Kraken saying that it was increasing the number of confirmations required to make an ethereum classic deposit, and Poloniex has disabled all ETC wallets.