Apple CEO Tim Cook explained to ABC News anchor David Muir why he refused to create software that would help the FBI break into an iPhone used by one of the San Bernardino, California, shooters. "I think safety of the public is incredibly important -- safety of our kids, safety of our family is very important," Cook said. "The protection of people's data is incredibly important, and so the trade-off here is we know that doing this could expose people to incredible vulnerabilities.