If yours is a cold wallet, you are immune to cyber viruses – because your wallet, by definition, is not connected to the internet. But eventually, you will connect that cold wallet to the internet (to sell or transfer your coins), and at that point, your cold wallet becomes a hot wallet – and subject to the risks you describe. There’s no way to avoid this risk, but I’d consider it to be extremely low – so low that you never hear about incidents such as those you describe. I think you’re catastrophosizing – scaring yourself by focusing on unlikely events instead of focusing on more realistic events (such as bitcoin quintupling in price). You might as well suffer insomnia by worrying about asteroids hitting Earth.