I guess when the FBI compels them again That's a bit of a specious argument though – of course, if they produce different software in the future, it could be u

I guess when the FBI compels them again That's a bit of a specious argument though – of course, if they produce different software in the future, it could be used again! If the FBI want their own ability to sign Apple updates, then that's obviously a different situation. But the point you were making – that it's not possible to write software that will run on only one device – is not true in this case. This is not mysterious. Can the FBI require a software company to subvert their own security guarantees? Should they? Do bank vaults have back doors for the FBI? I don't really know the right answer.