When will we not worry about terrorism?

I never imagined in my youth that the biggest threat to peace in this world would be terrorism. The thing about terrorists is that they don't necessarily look any different than anyone else(so they're hard to detect), they don't necessarily all stay together in one location(so they're hard to eliminate or isolate) and they never seem to have a justifiable reason for their violent actions. But they do seem to have an ongoing and endless group of individuals who are willing to join them and partake in their activities. That is why I believe that we may never be able to "not worry" about where and when a terrorist action will take place. Even if you are able to kill a group of terrorists, you can't get them all. It's like trying to kill every ant in an ant mound. Some will survive and regroup to terrorize another day. Whenever I visit New York City, it's always in the back of my mind that Manhattan is an excellent spot to detonate a nuclear bomb in order to kill off the most people in a small area. As I'm walking the city streets with my wife, I'm thinking "with our luck, this will be the day that a terrorist group sets off a bomb of that magnitude". I strongly believe that with all the nuclear bombs that currently exist is this world, one will eventually be acquired by terrorists who will try to use it. There is certainly a possibility that it will never happen but (for some undetermined reason) the terrorists want to inflict as much pain and suffering as they possibly can and have no feelings (other than accomplishment) for what they have done and obviously, they would like to top the actions commited on Sept. 11, 2001. I fear these despicable human beings will continue to be among us for many more generations so even if we all have to tolerate extensive security measures everywhere, we just have to accept that this is the way of life for now on and pray that no evil plans of terrorists are ever successful.