Viruses can be surprisingly elegant things. While some, such as CMV, contain as much genetic material as some bacteria, others have the bare minimum to be able to enter a cell and reproduce. It's tempting to think of viruses as incredibly cunning organisms - in fact, it's probably more accurate to think of them as a self-sustaining chemical reaction which happens to involve animal cells. Viruses don't think, yet are capable of defeating a highly evolved immune system and everything modern science can throw at them. I find them both terrifying and strangely attractive. See prions for the logical continuation of simplifying infective bodies, and become somewhat concerned.