In Outbreak, you will guide the spread of an aggressive virus, which attacks the host's cells, and turns them into copies of itself. Those copies then aid the spread, until all the host cells are gone. However, the host's immune system will present you with many problems, like forcefields which kill off all but the pure original virus cell, and fighter cells, which will patrol and kill virus cells on sight. You must use all your cunning and skill if you are to win.
Thanks for signing up for the Outbreak early access beta - by signing up, you will now be one of the first to play the game, and you're getting a chance to give feedback, that will shape how the rest of the game is made. Note that the game is not yet finished, and that there are currently only 6 levels available, with a fairly steep learning curve. That will of course change in the final version.