Some virus experts might not consider viruses to be alive. Yet viruses can reproduce. To do so, they hijack the cells of a host. They borrow the “machinery” in the host’s cells to copy the virus’ genetic code. Those host cells may spit out hundreds or thousands — even millions — of copies of the original virus. These new viruses then go on to infect more cells. Maybe the host will also sneeze out the viruses or otherwise release some to infect other potential hosts. And those hosts might be anything from people or plants to bacteria.