slightly OT, but can electrum sweep a key 'offline' - i mean can the sweep be initiated on an offline wallet and then loaded onto an online machine ?
cos i'm wondering if the sweep function is vulnerable to some form of attack if done on an online machine, as you're sweeping a private key...
It can't be done on an offline computer. But it can be done in a watch-only wallet on an online computer. So the private key of the target address can be on an offline PC. The private key you are sweeping would still be exposed though.