iOS users who have had their devices repaired by a third-party service may be in for an unpleasant surprise when they try to update their phone’s software. According to a report from The Guardian, Apple has recently confirmed that the “Error 53” message that has had people up in arms is actually the company’s clever way of preventing Touch ID-related security breaches.

The error has been the talk of online forums for more than a few months now, but Apple has only recently explained what’s going on. The message reads, “An unknown error has occurred (53),” and the device dies out shortly after.

Thousands of complaints about Error 53 messages from iPhone 6 users had reported their devices were now “useless bricks” on Twitter and on Apple’s online support forums. The company, in a statement to the Guardian, confirmed that the phones will shut down if a non-licensed technician performs a repair on the device.

It affects iPhones where the home button with touch ID fingerprint recognition built in has been repaired by a third party. It can also happen to users whose phones have sustained damage but are still at least somewhat useable.

The killer message doesn’t appear until a user with a repaired or damaged phone tries to install the newest iOS software, 9. Phones that were otherwise working fine suddenly failed to turn on when the update triggered the security mechanism.

Apple supposedly knows about the problem, but has done little to address it thus far. The security measure is probably not a bad thing to have in place, as it may indeed be possible to tamper with the Touch-ID fingerprint recognition function and break into someone’s iPhone to steal sensitive information.

According to a spokeswoman from Apple, “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 unauthorised 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 has a page on what to do if your phone displays the “Error 53” message. It can be found here.