The attack that the FBI is trying to facilitate by getting Apple to make a custom OS would only work up to the iPhone 5C and earlier models. Any iPhone with the TouchID and Secure Enclave would not be susceptible to this attack (it may be to other attacks). The Secure Enclave has a hardware enforced back-off delay that would stop the brute force attack. The older iPhone 5C does not have the Secure Enclave so the brute-force protection is implemented in the operating system. As such, Apple can load a new OS on the phone that does not have those protections.<p>Here is a great technical rundown: <a href="https:&#x2F;&#x2F;blog.trailofbits.com&#x2F;2016&#x2F;02&#x2F;17&#x2F;apple-can-comply-with-the-fbi-court-order&#x2F;" rel="nofollow">https:&#x2F;&#x2F;blog.trailofbits.com&#x2F;2016&#x2F;02&#x2F;17&#x2F;apple-can-comply-wit...</a>