Blockchain reorganization attack on Bitcoin
This Attack on Bitcoiner submits to the merchant/network a transaction which pays the merchant, while privately mining an alternative blockchain fork in which a fraudulent double-spending transaction is included instead. After waiting for n confirmations, the merchant sends the product. If the Attack on Bitcoiner happened to find more than n blocks at this point, he releases his fork and regains his coins; otherwise, he can try to continue extending his fork with the hope of being able to catch up with the network. If he never manages to do this then the Attack on Bitcoin fails, the Attack on Bitcoiner has wasted a significant amount of electricity and the payment to the merchant will not be reversed.
Also called alternative history Attack on Bitcoin. This Attack on Bitcoin has a chance to work even if the merchant waits for some confirmations, but requires relatively high hashrate and risk of significant expense in wasted electricity to the Attack on Bitcoining miner.