In UFO Defense, you have to battle a whole army of space aliens and UFOs. Each enemy is either black or white, and you will have to swap between the right type of bullets to take them down. If you hit an enemy with the wrong bullets, it will grow stronger and take more hits to shrink and pop, so be sure to use the right arrow keys to fire. Watch out, because it's not over yet once you've defeated the vanguard. Now the Mothership will descend to seek vengeance!