Apple has solved a problem of its own making, issuing a new revision of its mobile device operating system after a previous update rendered some iPhones and iPads unusable.
The tech giant has released a new build of iOS 9.3, numbered 13E5237, which it believes can safely be installed on older devices. It replaces the 13E234 on the iPhone and 13E233 on the iPad.
With features including Night Shift, Touch ID for Notes, greater personalisation for the News app, new Apple Music options for CarPlay, more Quick Actions for 3D Touch and several iOS in Education enhancements, the release of the latest OS last week was greeted with delight by Apple users.
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However, the upgrade did not go well for some. A bug, which mostly affected iPad 2 models, "bricked" the devices, leaving them unusable and displaying the following error message: "Your iPad could not be activated because the activation server is temporarily unavailable. Try connecting your iPad to iTunes to activate it, or try again in a couple of minutes. If this problem persists, contact Apple support at apple.com/support."
The message suggested the problem would fix itself in time but in reality, the devices were still inoperable days later.
Super-users sprung to the rescue, publishing complicated work-arounds online, although Apple now believes it has solved the issue by updating the OS.
These sorts of compatibility issues are only likely to get worse as Apple issues generation after generation of devices, experts say.
"With over one billion active iOS devices being used by consumers today, ensuring a bug-free experience will definitely be a major challenge for Apple going forward," says Forbes.
iOS 9.3: New iPhone features and how to upgrade
After seven betas, Apple has finally released its latest version of iOS after an announcement during the firm's keynote event at Cupertino, California, on Monday.
iOS 9.3 is more than a few tweaks and fixes – all new features include educational tools as well as the promise of a better night's sleep.
The free update is available for the iPhone 4S or later, iPad 2 or later, all iPad Minis, iPad Pro and iPod Touch fifth-generation and onwards.
So what should you look out for?
One of the biggest features introduced is Night Shift, a colour balance feature which changes the warmth of the display hues to match the time of day.
Blue light at night can affect levels of the sleep-inducing hormone melatonin, making it harder for your brain to switch off, so Night Shift tracks sunset and moves the colours on the display to the warmer end of the spectrum so they are easier on your eyes. Many third-party apps have done this before, but now it's an official part of iOS.
Added security for Notes
In a great step forward for those who use Notes to store sensitive information such as credit card details, the updated operating system will now lock the app away behind new security controls. Touch ID will let you use your fingerprint to do this but if your device is a little older, passcodes can be used, too.
3D Touch updates
In an upgrade which only concerns iPhone 6S owners, Apple has introduced some new 3D touch shortcuts for the App Store, Compass, Health, Weather and iTunes. According to Forbes, drip-feeding new 3D Touch upgrades into the iOS ecosystem will become a vital aspect of system updates in the future as the "patchy" integration means users cannot yet use the feature instinctively knowing it will work across all apps.
"If Apple wants 3D Touch to truly take off it needs to up its game" as users will expect it to work everywhere, says the site.
An iPad update, Apple has made changes to the way its tablets can be used in educational environments, allowing them to be shared more easily across a group of students as well as providing a new classroom companion app for teachers.
iPads now have multi-user support optimised for the classroom, enabling students to log off one device and log on to another and find everything – photos, books, documents – where they left it. The new Classroom app will allow teachers to control every iPad in the room and see what students are up to via a screen-view feature. There's also a new Apple School Manager to help teachers organise entire classes.
Other updates and fixes
Apple Health gets an upgrade, providing greater visualisation of the data it collects and more information on workout and weight-tracking, among others. There's also CarPlay updates and added personalisation to Apple News.
Fixes include one correcting a glitch that displays incorrect battery levels and a solution to the problem that bricked devices if the date was set to January 1970, something many users were tricked into doing.
How to upgrade
Compatible devices will be prompted automatically to upgrade. However, it can also be accessed by opening up the device's settings, pressing "General" and then selecting "Software Update" or downloaded through iTunes.
Owners of jailbroken machines be warned – a version of the software has yet to emerge that you can use.
Create an account with the same email registered to your subscription to unlock access.