Predators scouring the Internet, targeting children for sex: It's a national problem that Dateline has helped uncover. We got such an overwhelming response from our last investigation— some 15,000 emails from parents, grandparents, teachers and law enforcement— telling us to "keep up the good work," and "keep the issue alive." On Wednesday night, April 26, Dateline is back with the fourth undercover investigation. This time, we traveled to small town America. Even far from the big cities and suburbs, vulnerable young teens are not far from danger. A warning: some of what you're about to see is explicit.