Before this update, Vine was rated for anyone 12 and older. But that became increasingly risky as users began uploading and sharing pornographic content.
A simple search for #sex or #porn would bring up an array of graphic video. At one point, Vine accidentally featured a pornographic video to all of its users, which prompted Apple to remove the app from its "Editor's Choice" section on the App Store. After that, Twitter started blocking all porn-related searches. However, it's still pretty easy to find porn on Vine with some clever searching techniques.