The FBI is in the midst of investigating a married couple who killed 14 people in a mass shooting in San Bernardino, California, in December. The pair was believed to be inspired by the terrorist group, the Islamic State or ISIS, but it's unclear how deeply the pair is tied to foreign militant groups, according to Reuters.
Messages on shooter Syed Rizwan Farook's iPhone may, or may not, shed light on their terrorist ties. But the phone is locked by a pass code, and by default, these phones are programmed to erase data after too many unsuccessful unlocking attempts. The FBI didn't want to risk trying to hack the phone and losing all the data in the process.
Read MoreWhy Apple is fighting the FBI's San Bernardino investigation
Up until now, Apple has helped the FBI with the case, the company said. But it has resisted one specific request: To make a new version of the iPhone operating system and install it on an iPhone to make it easier to unlock by trying millions of password combinations without erasing the data within.
A federal magistrate ruled Tuesday that Apple must create this highly specialized software within a certain time frame. But Apple CEO Tim Cook released a letter saying he would challenge the FBI's demands.
Read MoreThe 'esoteric' law being used to fight Apple