In order for an organism to be considered living it must be able to reproduce on with its own species or on its own, (sexually and asexually) which is why we consider viruses not to be living.
Viruses are not made out of cells, they can't keep themselves in a stable state, they don't grow, and they can't make their own energy. Even though they definitely replicate and adapt to their environment, viruses are more like androids than real living organisms.
