Coinbase, Poloniex, Kraken disable Ethereum Classic deposits and withdrawals following chain reorganisation

Cryptocurrency exchange Coinbase has announced that it has suspended all ethereum classic (ETC) transactions, withdrawals and deposits after detecting a deep chain reorganization of the blockchain, CoinDesk reported.

According to block explorers – Bitfly (Etherchain) and Blockscout, ETC saw reorganization of over 100 blocks during a potential 51 percent attack late Sunday.

We can confirm that there was a successful 51% attack on the Ethereum Classic (#ETC) network with multiple 100+ block reorganization. We recommend all services to closely monitored the chain and significantly increase required confirmations.
— Bitfly (@etherchain_org) January 7, 2019

In a blog post, Coinbase said:

“On 1/5/2019, Coinbase detected a deep chain reorganization of the Ethereum Classic blockchain that included a double spend. In order to protect customer funds, we immediately paused movements of these funds on the ETC blockchain. Subsequent to this event, we detected 8 additional reorganizations that included double spends, totaling 88,500 ETC (~$460,000).”

Coinbase further said that it stopped interacting with the ETC blockchain upon observing this reorganization and added:

“Coinbase was not the target of this double spend and no funds were lost.”

In a tweet, the team behind ethereum classic said that they are now working with Chinese security firm SlowMist and others and recommended exchanges and pools to significantly increase confirmation times.

To be clear we are making no attempt to hide or downplay recent events.

Facts are facts and as the situation develops we'll soon get a full picture of what actually took place.
Linzhi is testing ASICS. Coinbase reported double spends; both may be true.

In time we will see. https://t.co/bbq6eqIoiS
— Ethereum Classic (@eth_classic) January 7, 2019

Ethereum classic dev advisor Cody Burns told CoinDesk that the activity could not be called a 51 percent attack. He explained in a tweet:

“Chain reorganization is a client-local phenomenon; the entire Ethereum network doesn't "reorganize" simultaneously. It would be more likely that someone discovered all of coinbase etc nodes and 'surrounded' them.”

Cryptocurrency exchange Kraken has announced that it has disabled ETC funding and said, “Funding will be resumed when the network's health has stabilized. Trading continues, for now.”

Poloniex said, “Due to a potential 51% attack, ETC wallets have been disabled and will not be re-enabled until tomorrow (at the very earliest). We will update this thread when we have a firmer timeline for re-enabling deposits and withdrawals. Poloniex was not affected, and your fund are safe.”