Apple has stopped signing iOS 8.4 for iOS devices. Users can no longer upgrade or downgrade to that version using iTunes. iOS 8.4.1 is the earliest version now being digitally signed by the Cupertino firm.
iPhone, iPad or iPod touch users that have jailbroken their device on iOS 8.4 should refrain from updating to iOS 8.4.1, as the latest software update breaks the iOS 8.4 untethered jailbreak released in June by Chinese hacking team TaiG.
While an 8.4.1 untethered jailbreak was demonstrated last week by Chinese hacking team Pangu, the method has not been publicly released. It is possible that the exploits used by the team were not patched in 8.4.1. It is also possible that the exploits used to jailbreak 8.4.1 can also be used to jailbreak iOS 9, so the team may choose not to expose it to Apple. For more information, visit the iPhoneHacks website.