Viruses: the ultimate mystery?

I remember as a child reading beyond the prescribed textbooks and spending hours in the library and encountering one of the very first completely mystifying things to me. Viruses.

Their existence seems completely mysterious. They are somewhere between "living" and not; they are built upon a system that must exist for them to "live" and reproduce - but what is the driving force for these pieces of organic matter to want to reproduce?

They have no mind or sense mechanism. No pleasure or reward system and yet the behaviour of these self contained units of DNA and RNA built with the proteins of their past host seems outright weird in the view of matter as without being or consciousness. Prions and smaller protein particles are possibly weirder still.

Are viruses the smoking gun for evidence of design in the universe?

Or are viruses just an accident or consequence of the complexity within the life process?

I can't say I know the answer to these questions but it's still a subjecy I think about a lot. Especially when I have a flu...