I find the iOS game "Plague Inc" pretty easy since the same tactic seems to work on every level.
I simply evolve air and water transmission along with cold and drug resistance until every single human being is infected. After that I just evolve coughing, "immunity something" and the next one giving me total organ collapse. The bodies hit the floor after that and the DNA points given during the downfall of society is invested in mitigating the effects of the cure. This tactic never fails me (I play normal difficulty) but it never seems to give me a better than average score (3 / 5 biohazard symbols).
What is the score based upon? Time to complete the level? % cure developed? If I completed the level with minimum evolution? Something else? Everything above?
If you don't know the above; Do you get higher scores? How?