While the FBI purchased a tool that allowed it to unlock an iPhone 5c used by one of the San Bernardino shooters, it appears that the usefulness of that tool is fairly limited. According to FBI Director James Comey, the tool can only access a small subset of iPhones, with the iPhone 5c being the most recent model that it will work with.
According to CNN:
"The FBI director also said the purchased tool worked only on a "narrow slice of phones" that does not include the newest Apple models, or the 5S. Comey said the government was currently considering whether to tell Apple how it pulled off the hack."We tell Apple, then they're going to fix it, then we're back where we started from," he said. "We may end up there, we just haven't decided yet."
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