YouTube has closed more than 400 accounts and deleted tens of millions more comments that it said were being used to promote the sexual exploitation of children. The move came after a YouTube user posted a video on Reddit Sunday focusing on what he called a “soft-core pedophilia ring” on YouTube. The post prompted outrage from a number of high-profile advertisers and caused a number of them, including Epic, Purina, and Disney, to pull their ads from the site earlier this week. YouTube now says it is working to catch the abuse more quickly. The question remains why YouTube waits until journalists and others identify questionable content on its service before YouTube removes it.