Following the release of iOS 13.3.1, Apple on Wednesday stopped signing code for iOS 13.3, effectively barring downgrades to the older operating system.
Apple's halt to iOS 13.3 code signing arrives two weeks after iOS 13.3.1 was issued in late January.
With Apple no longer authenticating iOS 13.3 code, iPhone and iPod touch users are unable to download or install the out-of-date operating system.
Apple routinely stops signing legacy code after the release of a new iOS build in part to protect customers from nefarious actors attempting to take advantage of newly discovered vulnerabilities. In addition to security, preventing users from downloading older code allows Apple to keep more iOS devices on the latest, feature-rich software.
The current iOS release, iOS 13.3.1, fixes a number of bugs including a flaw in Communication Limits that allowed new contacts to be added without first entering a Screen Time passcode. Apple also addressed a minor privacy controversy by adding an option to disable location services for iPhone 11's U1 Ultra Wideband chip.
Other issues patched in iOS 13.3.1 include a slight delay when taking Deep Fusion photos on iPhone 11 and iPhone 11 Pro, a Mail bug involving the loading of remote images, push notification failures and distorted CarPlay audio. The update also introduced Indian English Siri voices for HomePod.