Following the July 19th release of iOS 10.3.3, Apple has this evening stopped signing iOS 10.3.2. It means that, from this point forward, users will no longer be able to upgrade or downgrade their devices to iOS 10.3.2.
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In almost every case, Apple stops signing older firmware shortly after the release of updated firmware. Doing so is a gentle way of nudging users to the latest and greatest version of iOS when performing upgrades, and prevents users from downgrading to older versions.
The motives behind Apple’s decision to stop signing older firmware are multifaceted, but the short and sweet of it is that it wants users to have the latest features, and more importantly, the latest security updates on their devices.
Closing the firmware signing window is also a good way to help thwart jailbreaking, because Apple closes the vulnerabilities associated with those jailbreaks, and effectively forces users to fixed, newer firmware upon a restore. It’s one reason why jailbroken users, or those wishing to potentially jailbreak, are often hesitant to update to newer versions of iOS.
If you’re looking to verify the signing status of a particular device, then IPSW.me is a great resource for doing so.