Preheat Oven to 350 degrees. Grease and flour a 10-inch Bundt Pan.
In large bowl combine cake mix, frosting, eggs, oil, water and beat on low for 30 seconds. Beat on medium speed with electric mixer for 2 minutes
scraping bowl occasionally. Fold in 1/2 cup of pecans and 1/2 cup of toffee bits.
Sprinkle the remaining 1/2 cup of pecans into prepared Bundt pan, pour batter over pecans.Level batter by holding pan 3 or 4 inches above counter, then dropping it flat onto the counter. Do this several times to release air bubbles and assure you have a level cake.
Bake for 55 minutes or until toothpick inserted in center of cake comes out clean.Cool for 15 minutes; remove from pan to cooling rack. Cool completely.
In a 1-quart saucepan, melt butter over medium-high heat. Stir in brown sugar, corn syrup and milk, stirring frequently. Bring to a rolling boil, remove from heat, and immediately beat in powdered sugar and vanilla with wire whisk until smooth. Immediately drizzle over cake, sprinkle with toffee bits. Store loosely covered at room temperature.