" Most people think of viruses as parasites, but they aren't parasites at all. An organism has to be considered alive to be classified as a parasite. Viruses don't do any of things living organisms do. They don't grow, they can't move on their own, and they don't metabolize. They don't even have cells. But the one thing a virus is very good at is reproducing. When it finds a suitable host cell, it attaches itself and injects its DNA through the cell's plasma wall. The virus's genes are transcribed into the host cell's DNA, and the host cell's genetic code is rewritten. Whatever its job was before, its new job is to do nothing but produce copies of the original virus, usually until it's created so many that the cell bursts open and spreads the infection. "

― Christian Cantrell