Bake cake as directed on box. Grease and flour the bottom only of a 13 x 9 inch pan. Pour cake into prepared pan and bake according to directions.
When cake is done baking, cool on rack for 5 minutes. Meanwhile, prepare the pudding as directed on the box. With the handle of a wooden spoon, poke many holes in the warm cake. Spread all the pudding over the cake with a spatula, carefully pressing the pudding into the holes. You will still have a layer of pudding on top of the cake. Cover and refrigerate for at least an hour.
Uncover the container of chocolate frosting. Microwave for approximately 20 seconds. Stir well and pour over the pudding layer. Spread to the edges and refrigerate another hour before serving.