Software capable of unlocking an iPhone 5C or older has been leaked
Last year, the FBI ordered Apple to help break into the iPhone 5C owned by Syed Farook, one of the shooters in the 2015 terrorist attacks in San Bernardino, California.
Apple refused, with CEO Tim Cook describing the backdoor requested by the FBI as the "software equivalent of cancer".
"This is not about one phone," Mr Cook said back in February 2016.
"This case is about the future. Can the government compel Apple to write software that we believe would make hundreds of millions of customers vulnerable around the world?
"In the physical world, it would be the equivalent of a master key, capable of opening hundreds of millions of locks — from restaurants and banks to stores and homes," he later added.
"No reasonable person would find that acceptable."
CEO Tim Cook published the open letter on the US technology company's homepage
Apple also published an open letter on the homepage of its website, criticising the FBI request.
"They have asked us to build a backdoor to the iPhone. Specifically, the FBI wants us to make a new version of the iPhone operating system, circumventing several important security features, and install it on an iPhone recovered during the investigation.
"In the wrong hands, this software – which does not exist today – would have the potential to unlock any iPhone in someone’s physical possession," the letter read.
However, the FBI did manage to unlock the iPhone 5C.
The US government agency is believed to have worked with Cellebrite, an Israeli firm that specialises in mobile security, to unlock the mobile phone without Apple's help.
According to a statement published by Cellebrite last month, a hacker managed to breach one of its legacy servers.
And now that hacker has released some of the stolen data as a warning to the FBI – reiterating what Apple CEO Tim Cook cautioned could happen if the Cupertino company build the iOS backdoor.
The leaked data includes code relating to Cellebrite's Universal Forensic Extraction Device, or UFED, which is allegedly able to crack into an iPhone 5C or older, as well as Android and Blackberry devices.
A previous Motherboard investigation found US State Police and Highway Patrol agencies have collectively shelled out millions of dollars on Cellebrite technology.
On PasteBin, the hacker taunted "@FBI be careful in what you wish for"
Speaking anonymously, the hacker explained that building this type of software makes its release inevitable.
Once the software is released in the wild, it can be used by anyone – including oppressive regimes across the globe.
"It's important to demonstrate that when you create these tools, they will make it out.
"History should make that clear," the hacker told Motherboard.
The hacker claims to have lifted the tools from the Cellebrite servers, and claims to have accessed the encrypted files and shared the information on Pastebin – a popular code repository.
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However, a spokesperson for Cellebrite told Motherboard that the files shared on the code repository did not actually include the source code, only packaging information.
"The files referenced here are part of the distribution package of our application and are available to our customers.
"They do not include any source code," the spokesperson told Motherboard.
Although the code leaked online does not include the exact method to break into current device models, the warning from the hacker is clear – these tools never stay private for long.