Apple iPhone 6 and Apple iPhone 6 Plus users are losing their phones to "error 53"

Whatever the reason, let this be a warning to you. If your iPhone 6 or iPhone 6 Plus is damaged, you might want to consider allowing Apple to handle the repairs. Otherwise, "error 53" could leave you with an expensive paperweight.
"We protect fingerprint data using a secure enclave, which is uniquely paired to the touch ID sensor. When iPhone is serviced by an authorised Apple service provider or Apple retail store for changes that affect the touch ID sensor, the pairing is re-validated. This check ensures the device and the iOS features related to touch ID remain secure. Without this unique pairing, a malicious touch ID sensor could be substituted, thereby gaining access to the secure enclave. When iOS detects that the pairing fails, touch ID, including Apple Pay, is disabled so the device remains secure...when an iPhone is serviced by an unauthorized repair provider, faulty screens or other invalid components that affect the touch ID sensor could cause the check to fail if the pairing cannot be validated. With a subsequent update or restore, additional security checks result in an ‘error 53’ being displayed … If a customer encounters an unrecoverable error 53, we recommend contacting Apple support."-Apple
source: TheGuardian