Apple's production lines are so massive that it's easy to imagine iPhones being smuggled out of there.

We all know the story of the prototype iPhone 4 that was left at a bar, spoiling what could have been one of the biggest surprises in Apple history. But have you heard the one about the stolen prototype iPhones that are still winding up in unintended hands — in this case, hackers bent on finding ways to break into Apple’s operating system?

As per a report, some of the most prominent iOS hackers have made use of prototype iPhones to break into iOS.

Just like every smartphone maker, Apple also develops a prototype or 'dev-fused' iPhone for testing different technologies, modems, chips.

If you are an iPhone user, chances are that you know about Cydia, the jailbroken app store for iPhone and iPads. While Jailbreaking is a type of hack that is mostly used to sideload paid apps for free, there are other types of hacks as well. Hacks that are either much more problematic or useful, depending on which side of the hack one is in. Apple phones come with a Secure Enclave Processor (SEP) that encrypts sensitive data on the phone and is set-up as a separate entity. Motherboard investigated how some of the best hackers were able to get study the chip and the answer is said to be a “dev-fused” iPhone, which is an iPhone that was lifted before finishing the production process.

As per the report, these dev-fused iPhones are pre-jailbroken devices in which many security features are disabled. This is so that researchers can test them easily but these devices were never intended to get out of Apple’s reach.

The Motherboard report says there’s now a gray market for “dev-fused” iPhones and each product sells for thousands of dollars. Why? Because they help hackers, security researchers crack iPhones and find critical vulnerabilities in them.

Gaining root access to these pre-production iPhones is said to be much easier than doing the same on a commercially available iPhone.