One of China’s biggest Ethereum exchanges, Yunbi, addressed a loss of ETC due to a “Relay Attack” [Replay Attack]. Users were depositing ETH before the listing causing the exchange to lose 40,000 ETC.
Yunbi stated on their site:
The major reason of this lost is due to “Relay Attack” during the hard fork. YUNBI will not be responsible for this lost.
After YUNBI lists ETC, please make sure you use the correct address to deposit your ETC and ETH.
Because of the hard fork, the idea of a replay attack was plausible. Developers and exchanges were aware of the possibility since two similar chains will now exist. Either trading had to halt or be completely redone to avoid double or lost transactions.
Timon Rapp, a software developer for Kraken, explained how a relay attack can occur with these two chains:
“Every transaction that happens on the ETH network is a valid transaction on the [ETC] network and vice versa. When every transaction gets relayed to both networks then they will move funds on both chains in the same way unless they involve the ETH from the Dark DAO which did not leave the Dark DAO on the old chain.”
The reason for this is those who had ETH before the fork now have the same amount of ETC on the original chain. This means if you are to trade ETH or ETC around on an exchange that does not fully support either one or both, your funds will be lost.
This kind of damage scared many Ethereum exchanges away from associating with ETC. Many assumed one chain would fade away.
But with the high demand for ETC, exchanges such as Poloniex, Bittrex, Kraken and Bitfinex have added ETC to their trading platform.
Yunbi has enabled trading of ETC on their platform. As for the lost ETC, Yunbi will reimburse their users.