iOS 9 is rolling out several security improvements, under-the-hood refinements and developer-designed features that promise better user privacy and security. The operating system improves two-factor authentication by building it directly into iOS. The passcodes you use on your Touch ID-enabled device will have to be six-digits long, to counter brute forcing attacks. A new feature called App Transport Security (ATS) encourages developers to implement HTTPS to secure communication between apps and web servers. Apple also implemented Rootless,. a kernel-level security feature that limits admins access to certain kernel files.”]
Source: https://www.bitdefender.com/blog/hotforsecurity/read-all-about-it-nine-security-novelties-in-ios-9/