A virus is something so strange and alien that we don't really know what to make of it. It's a bizarre collection of molecules, configured in such a particular way that enables it to kill you. The fact that opinions differ on whether a virus is alive or not tells you something about the mysterious nature of these things. Although they posses genes and evolve by natural selection, they don't have their own metabolism or even a cell-wall or cell-structure for that matter. Unlike normal life it does not reproduce by mitosis (division) but through spontaneous self-assembly. They are said to be right at the edge of life and their ability to just pop into existence out of chemical soup provides key insights into how the earliest life might have come about.
The hidden world of the virus exposed... Beautiful isn't it?