Seth didn't really have to hack it. He worked as a developer for them. Was working on an app for voting locations and noticed Hillary had ones that are set aside for only her voters, to make election fraud more easy. You only adjust votes at places where your voters didn't go as much, and leave your exclusive voter locations untouched. Seth was a Bernie fan and this pissed him off greatly. So he took emails probably just using administrative credentials. Although it is said that podesta was phished as well. Not sure if that's same occurrence or a different one.