Imagine a virus with the effect and latency period of HIV that could be spread by a sneeze. Viruses are hard to describe. As long as it isn't inside a computer's operating system, it's harmless, dormant, abstract. Once the code is in a computer, however, it does three things. It acquires a host, it begins to make the computer run wrongly, and it can reproduce itself to spread to another computer.
Biological viruses are similar.
Outside living cells, they're not much more than a piece of information, a scrap of nucleic acid in an envelope of protein. But even if the HIV virus were one day wiped from the face of the earth, it would still be possible to write down the chemical sequence required to recreate it in a string of letters about as long as this article. The goal of a virus is to break into a cell, use the cell's facilities to reproduce itself, and then spread to the next host. I say 'goal', because it is hard not to see viruses as ingenious workers towards an end, so cunning are their methods. Colds and flu make you sneeze in order to spread themselves.