Apple on Wednesday stopped signing code for iOS 13.6, effectively preventing users who updated to the latest iOS 13.6.1 release from downgrading.
Issued last week, iOS 13.6.1 includes a handful of bug fixes including a patch for a thermal management issue that would in some cases cause an iPhone's screen to display a green tint.
The release also remedied a problem with Exposure Notification alerts and an issue that prevented the deletion of unused system files.
Today's code signing stoppage means users can no longer download the out-of-date iOS 13.6 operating system from Apple's servers. Apple regularly ceases signing of older code to prevent installation of past iOS versions following the release of a new version in a bid to keep users safe from new threats. The practice also ensures devices are running the latest feature-rich software.