Keeping kids safe?

I have a 5 year old daughter and I don't feel comfortable letting her play alone in the back yard even though we've gone to great lengths to childproof it and have a fence. My worry is child preditors. If she was playing in the back yard, of course someone would watch her from in the house, but you hear all the time about kids getting abducted these days and the parent just turned their back for a moment. Am I the only one with these fears and is there an alternative so that my daughter can be more active? I don;t want her to sit and watch TV (or even read) all day. I also wanted to add, that when I was 5, my parents did let me play in the back yard, alone and they didn't watch me like a hawk. Why, do you think, is it so much scarier these days?