FBI = Feral Baboons of Incompetence
The Feral Baboons of Incompetence have not figured out that by destroy an OS because they are too lazy to get out of the donut shop sets a precedent that they can destroy any proprietary OS. The only way Apple or Slurp can prove there are not backdoors would be to open source their respective OSes. As long as the OSes are proprietary there can be a backdoor very quietly hidden but with an open source it is much harder to hide, the code being available to all.
Ironically, W10 may be the last true Winbloat and OS X may return to FOSS roots.
Biting the hand that feeds IT
