the aim of space invaders is to shoot down all the aliens who are slowly moving down from the top of the screen to the bottom. if you can do this before they reach your shooter and you can avoid being shot more than twice, you win.

use the left and right arrow keys to move your shooter left and right (or you can use J and L if you prefer). to shoot, use the space bar (or the enter key). press P to pause the game.

the top left of the screen shows you how many lives you have left. the top right shows you your score. every so often, a spaceship flys across the top of the screen. if you shoot this, you get a random bonus score. this is what scores are available:

 = 10 points
 = 20 points
 = 30 points
 = 50, 100 or 150 points

you also get a bonus 100 points at the end of the game for every life you have left. so this means if you dont get hit at all, you get an extra 300 points for having all 3 lives left.

you can hide under the green bases to avoid being shot by the aliens, but each time a base gets hit some of it erodes until there is none left. the more aliens you kill, the faster they move and so it becomes increasingly harder to shoot them.