I am putting the final touches to my new iPhone game called iBody Defence.  You control a small craft around the inside of a human body and collect up nasty virus which are floating about.

As you are also a foreign body inside the patient, you have to avoid the red and white blood cells which are on patrol.  These will attack you as well as the virus.   Each virus you collect and drop off at the Virus Collector, earns you money.  The more you collect, the more money you earn.   If the blood cells on patrol attach and kill virus then you will have money deducted from your paycheck!