So if they can figure out the private key of him. Means that, none of our private key is safe here?
Sorry for this conclusion, but it makes me wonder. Imagine if i want to solve someone private's key but pretend that it's my address?
Privatekeys have dozens of letters. They are not bruting force all of them, but 8. And it is not brute Force simple, as coding enthusiast pointed out.
Your conclusion is completely wrong because private keys are composed by dozens of letters, not 8only.