Excerpt from an interview with John McAfee
Interviewer: “Is there any way to secure your bitcoins once you have earned them?”
"Absolutely! I think mine are secure. But the only way to do it is offline. You can buy devices, my favorite one is Trezor and the reason is, is because your seed keys. When you first create a wallet it gives you a thing called seed keys. Its a list of words, random words. Car, shoelace, dog, cow, whatever. These are your seed keys. Randomly generated to the point that theres no way anybody could ever guess them in the right order.
… Whats nice about the Trezor device, is it has a tiny little screen that shows you the seed keys on this screen not your smart phone, not your laptop, not your desktop. But on that device. So no hacker can access them. Then once you put your bitcoin into the wallet, unplug it, bury it in the back yard, hide it under your mattress, whatever you want to do with it like it was real cash.
But to keep the wallet on any intelligent device (referring to online wallets) whether its your laptop, desktop or any mobile device is insane, it will get stolen.”