If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).
Destroy alien invaders by bouncing your shots off the walls, You have many chances to save the earth.
Arrow keys left / right - To move.
Arrow keys up / down - To navigate special weapons menu.
Space bar - To shoot.
Control key - To deploy / activate special weapons.
P - To pause / resume.