Electrum is a thin client that has to ask a full node for the chain so that it can pluck out the relevant transactions to rebuild your local wallet state. http

Electrum is a thin client that has to ask a full node for the chain so that it can pluck out the relevant transactions to rebuild your local wallet state. https://en.bitcoin.it/wiki/Thin_Client_Security https://en.bitcoin.it/wiki/Thin_Client_Security It knows which transactions are relevant because of the keys that can be deterministically generated from your seed, but the seed itself isn't sent to a server.