Recently there has been a big issue going on where if you replace the Touch ID sensor at an unauthorised Apple repair shop, the device disables itself.
Many customers were frustrated about the issue, and Apple has released a patched version of iOS 9.2.1 to fix the issue today.
According to TechCrunch, Apple says the Error 53 issue was designed to be a factory test and not to affect customers.
Some customers’ devices are showing ‘Connect to iTunes’ after attempting an iOS update or a restore from iTunes on a Mac or PC. This reports as an Error 53 in iTunes and appears when a device fails a security test. This test was designed to check whether Touch ID works properly before the device leaves the factory.
Today, Apple released a software update that allows customers who have encountered this error message to successfully restore their device using iTunes on a Mac or PC.
We apologize for any inconvenience, this was designed to be a factory test and was not intended to affect customers. Customers who paid for an out-of-warranty replacement of their device based on this issue should contact AppleCare about a reimbursement.
You can grab the updated version by connecting your device to iTunes and doing an update.
However this will not restore Touch ID functionality. If you want Touch ID back, you will need to get the sensor replaced by Apple.