Apple has reportedly changed a part of iOS 5 to make it impossible for iPhone users to downgrade their phone’s firmware, even if they’d rather run an earlier version.

The iPhone Dev Team, a well-known group of iPhone hackers, first discovered the change in an unlocked developer’s version of iOS 5, which is expected to be released this fall.

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Normally, to restore your iPhone to an earlier version, you’d save “SHSH blobs” (which are like digital signatures to authenticate software) at a specific timestamp and use a third-party app to restore your firmware back to that time. The SHSH blobs are static and can be used as often as you like.

But the team found that in iOS 5, Apple has prevented people from being able to save these blobs for a specific timestamp. Instead, Apple will re-assign your phone a new SHSH blob each time your reboot your device in jailbreak mode, making saved blobs irrelevant since Apple can just reject ones that were saved.

This only affects untethered jailbreaks, so one way around it is to simply connect your iPhone to your computer and boot it up in jailbreak mode each time. But realistically, who lugs around a computer with their iPhones?

Furthermore, as the hackers note, this new system only applies to iOS 5.0 blobs and beyond. You’ll still be able to revert to pre-iOS 5.0 versions with your saved blobs, but from 5.0 onwards, there is no turning back.