The Ethereum (ETH) network experienced two anomalous transactions last week that sparked a rise in transaction fees, with the transaction senders being unidentified. However, yesterday on June 17, South Korean peer-to-peer cryptocurrency exchange Good Cycle stepped forward as the party behind the transaction.

On June 14, Ethereum mining revenue jumped by 46% as a result of a $2.7 million transaction fee that involved 350 Ether on June 11. Ethermine, the mining pool which processed the transaction, believed the transaction to be a mistake and waited a few days for the sender to come forward so that the transaction could be discussed.

However, none did, and Ethermine decided to distribute the transaction fee among miners. Similarly, another transaction of $134 worth of Ether with a transaction fee of $2.6 million was processed by Sparkpool.

Blockchain analytics and security firm PeckShield on Twitter said that Good Cycle was responsible for the transaction, and that it “appears to be a Ponzi scheme” and that it was vulnerable to hacks,

Good Cycle has said that it suffered attacks and that the exchange had sent transactions to Ethermine and Sparkpool with the message “I am the sender.” Vitalik Buterin commented on such attacks, saying that such hacks could blackmail an exchange by threatening to burn funds via high transaction fees.