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...
Electrum will need to connect to the servers to get all the transactions data of the address you're trying to sweep so no, you can't do it offline.
It should be safe unless you have a malware in your PC.