In September 2015 , Apple released a white paper detailing the security measures in its then-new iOS 9 operating system . The iPhone 5C model can be protected by a four-digit PIN code . After more than ten incorrect attempts to unlock the phone with the wrong PIN , the contents of the phone will be rendered inaccessible by erasing the AES encryption key that protects its stored data . According to the Apple white paper , iOS includes a Device Firmware Upgrade ( DFU ) mode , and that " r estoring a device after it enters DFU mode returns it to a known good state with the certainty that only unmodified Apple-signed code is present . " The FBI recovered an Apple iPhone 5C — owned by the San Bernardino County , California government — that had been issued to its employee , Syed Rizwan Farook , one of the shooters involved in the December 2015 San Bernardino attack . The attack killed 14 people and seriously injured 22 . The two attackers died four hours after the attack in a shootout with police , having previously destroyed their personal phones . Authorities were able to recover Farook 's work phone , but could not unlock its four-digit passcode , and the phone was programmed to automatically delete all its data after ten failed password attempts
2015 San Bernardino attack
2015 San Bernardino attack
FBI–Apple encryption dispute