Worries about fraud and fragmentation may prompt a shake-out in the crowded online-ad industry. THIS year, for the first time, advertisers in America may spend more online than on television. Worldwide, online ads may surpass television in 2017, predicts the forecasting unit of Interpublic, a giant ad agency. Digital advertisers’ ambitions border on the divine. They are omnipresent, nestling their ads in news sites, search results and Instagram feeds. They are increasingly omniscient: no longer do advertisers know just general things about you—a worldly professional, say, with superb taste in journalism—but they target you, specifically. Omnipotence, however, is proving harder to achieve.