1. download electrum
2. unplug your router
3. create a new wallet
4. export the pubkey to your mobile wallet of choice
5. delete the electrum file
6. plug your router back in
7. congratulations you have a completely Free ($$$) and FOSS cold storage wallet without having to buy any fancy hardware !
Deleting the file isnt enough.
Please free to add any extra information that could be useful to the crowd!
A key that ever existed on a computer that is later connected to the internet isnt provably better than a hot wallet.
I agree!
One level up is to boot a live linux disto on a diskless offline PC with a bitcoin wallet included - like https://tails.net/ for example
but still not good enough, only a bit better
