Many people are hooked on a new smartphone app from Japanese game company Nintendo. People have become so obsessed with Pokemon Go. Nintendo co-developed the game with an American venture firm. The app tracks the player's location with a smartphone's camera and GPS. It creates Pocket Monster characters and displays them against a background captured by the camera. The background changes as the user moves around, and players can catch the characters with the tap of a finger and have them fight characters controlled by other users. It's been the top-ranked app of download every day. But the craze has led to safety concerns. Japanese government is telling people not to play Pokemon Go while walking or driving.