When I create a transaction with Electrum on my computer, I use a hardware wallet to sign the transaction. When I sign the transaction, the hardware wallet shows the amounts, and the output addresses.
But if my copy of Electrum was backdoored and smart about what it did, it could use an output address for the remaining amount that went to another wallet. And since I and most people mainly check the address we are sending to but don’t pay close attention to the change address, we could end up having our funds stolen that way.
I’ve been thinking about moving to a multisig setup instead, that would have multiple computers independently used for checking and signing the transactions.
So far I’ve been putting it off because a single wallet and being diligent about checking the output address that you send to seemed sufficient. But now I think moving to a multisig setup is something me and more people should do sooner rather than later.