Kill enemies by pressing the corresponding letter on the computer keyboard. Hit SPACEBAR to drop a Panic Bomb that will destroy all the enemies on the screen at once. Kill Bonus Letters to complete the words 'LIFE' or 'BOMB' and get, respectively, an extra life or an extra Panic Bomb. Use the 'Pause/Break' key to pause the game. Kill the aliens as late as possible to get higher score (max 100).