First it was the bird flu. Then it was the swine flu. Guess what's next? That's right: the zombie flu!
You are a white blood cell. Your must protect the red blood cells. One way to do this is to bump them out of harm's way. The other way is to destroy the zombie viruses by moving over them. To help you do this, you can slow down the viruses or shrink them by shooting enzymes at them or by using Freeze or Time Bombs. Also, pick up as much RNA (green spots) as you can.
There are 3 types of zombie virus:
Dissolver (looks like a mouth): Destroys red blood cells; must be shrunk before they can be eliminated; can also shrink you and make it temporarily impossible to shoot
Eater (looks like a veiny eyeball): Grows by eating red blood cells
Spreader (looks like a black and yellow ball): Turns red blood cells into zombie viruses
WASD = Move
Left-Click = Shoot a Freeze/Shrink Enzyme
Space = Drop Freeze Bomb
Shift = Drop Time Bomb