Jailbreaks address a different type of vulnerability - that of incorrectly written code or poorly designed systems, that can lead to a privilege escalation. Th

Jailbreaks address a different type of vulnerability - that of incorrectly written code or poorly designed systems, that can lead to a privilege escalation. The vulnerability that the FBI are using is the ability of Apple to update the iPhone with arbitrary code, provided it has been signed with their secret key. It's an important feature, of course, but still a security vulnerability - albeit an irrelevant one for the vast majority of iPhone users.