"Old source code from three years ago appears to have been leaked, but by design the security of our products doesn't depend on the secrecy of our source code. There are many layers of hardware and software protections built into our products, and we always encourage customers to update to the newest software releases to benefit from the latest protections."
The iOS 9 source code for iBoot, the part of iOS that ensures a trusted boot of the iPhone's operating system, was leaked to GitHub but quickly removed after Apple filed a DMCA takedown request.
The leak doesn't affect users and and isn't an immediate cause for concern; however, it may help security researchers find vulnerabilities which could compromise a device or possibly contribute to a jailbreak.
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