Antpool prevailed in a brief Bitcoin chain reorganization at block 966500 on Sept. 11 after its valid block competed with Spiderpool's block, which was ultimately abandoned. Galaxy Research detected the event through its private node and said Bitcoin has experienced three one-block reorganizations in four weeks, including events at blocks 962722 on Aug. 16 and 963853 on Aug. 24. Such reorganizations occur when two valid blocks reference the same parent and the network follows the chain with more accumulated work. The security implications increase with depth: Monero experienced an 18-block replacement after Qubic released a withheld chain, while Bitcoin SV suffered a 100-block reorganization in summer 2021. Transactions in replaced blocks lose their confirmations, making deeper reorganizations a more serious blockchain security concern.