New digital-advertising formats such as those used by The New York Times, Forbes and Fortune allow advertising to ride along with articles during social sharing. But that presents a problem not only for tracking but for control over ad placement with respect to content, industry experts argue. "So 'Dr. Oz Fat Loss' could bid on Forbes' health and wellness articles; then you've got a problem. The publisher is in an environment someone else controls," says Peter Minnium, Interactive Advertising Bureau's head of brand initiatives.