support network that tp facilitated the hijackers and at that time they felt they had no direct knowledge of the plot, jenna. jenna: you almost want to knock on wood when you talk about it. why haven't we been hit again to the same magnitude that we saw on 9/11. >> reporter: for the most part current and former intelligence officials say it's been a combination of strong law enforcement. multilayered security, improved sharing and policies that have prevented another eye tack. we spoke to the nation security agency and the cia michael hayden. >> in my view, beyond the improved defenses, the single greatest factor we have going for us and keeping us safe is that we have taken this fight to this enemy, and we have attacked its leadership, we have attacked his leadership relentlessly and made him far less capable of