> An attacker can only try to change one of his own transactions to take back money he recently spent. ~ Satoshi Nakamoto in the [[Bitcoin Whitepaper.pdf|Bitcoin Whitepaper]] Transaction blocks are confirmed by nodes in the network at regular block time intervals, as dictated by the [[Difficulty]] algorithm. So, dishonest network participants attempting to spend money twice will have their transactions excluded on the basis of time-order. This feature is further ensured by [[Proof of Work]] requirements under which final consensus creates [[Immutability]].