user675: Does a Bitcoin node need to scan through the whole blockchain in order to be 100% sure that a transaction sent to it is genuine (especially when some inputs are derived from coins generated in the very early days)?

user85: Yes. It doesn't have to do all the work when it receives the transaction, of course. If it's in sync with the network, it's already scanned the whole blockchain.

675: <p>Does a Bitcoin node need to scan through the whole blockchain in order to be 100% sure that a transaction sent to it is genuine (especially when some inputs are derived from coins generated in the very early days)?</p>
 85: <p>Yes. It doesn't have to do all the work when it receives the transaction, of course. If it's in sync with the network, it's already scanned the whole blockchain.</p>
