It is still debated on whether viruses are alive or not. At one time they are floating around in the air, dormant, and then once they find a cell, they spring to action and attack it. Evidence for viruses being living are they contain DNA or RNA, which is what every piece of life has. And that DNA or RNA can mutate, or randomly change the sequence of its genetic material, which is also what all life does, including humans. They can also take over a host cell, by inserting its genetic material into it and taking over all of the functions of that host cell, causing it to make multiple copies of the virus. And after this process, the lytic cycle, the host cell bursts and new viruses are spread to other cells. So viruses have another characteristic of life, they can reproduce. Evidence for viruses being not living are that they do not fit all of the characteristics of life. They do not have their own cytoplasm or organelles, as they use their host cells for that purpose. They also cannot get food for themselves, or metabolize, as they use the host cell for this as well. And lastly, they can be crystallized like salt so if it is living, it shouldn't be able to do that.