It all depends on how you define "living" viruses can reproduce by themselves. They done "feed" they don't "mate" they just kinda sit there. The only time a virus does anything is when it enters the correct organism. And it is a theory that before complex singled cell life could exist viruses (or at least something similar to viruses) existed. Likely, simple DNA/RNA compounds surrounded by a very simple protein coat existed until they themselves gained more complexity to become single celled organisms. This kicking of evolution and life as we know it. But that's all theory and nice ideas.