: Once the attacker finds a block, they quickly send a second transaction—sending the same coins from Address A to the exchange's Address C—directly to the exchange's node.

: High; requires significant hash power and precise timing.

: This attack primarily targets services that accept one confirmation for high-value deposits.

: Once the exchange credits the account based on that one confirmation, the attacker withdraws the funds. Meanwhile, the rest of the network follows a different chain (where the original block was orphaned), and the transaction to the exchange is ultimately rejected as a double spend. Technical Context & Mitigation

: The exchange sees the transaction to Address C and then sees the attacker's block arrive. Because the block is valid, the exchange's node may count the transaction to Address C as having one confirmation , even though that transaction is not actually in the block.

The attack combines elements of a and a Race attack by leveraging a pre-mined block.