That is no definition. That just says that viruses are alive when they are viruses and dead when they are no longer viruses. Do you realize that they are not included in the classification system used for living things. Is a dead frog still a frog? According to your definition it would not be. You can do better than that.
You ask the question about viruses then take that answer into the context of frogs after rewording my definition. The rationale for what constitutes life for one segment of creation is not necessarily the same for another. Life is defined within the classification characteristics assigned to that classification.
This is simple grade school science and a rather stupid question for an adult.
It is like me asking you how you know that your brain is alive and not dead?
