Viruses don't fall into a domain and kingdom classification because they're neither prokaryotes or eukaryotes and aren't living
They're found anywhere there are cells to infect. Viruses have evolved to infect every form of life, from animal to plant and from fungi to bacteria.
Viruses are the simplest and tiniest of microbes; they can be as much as 10,000 times smaller than bacteria.
There are thousands of different viruses that come in a variety of shapes. Many are polyhedral or multi-sided, other viruses are shaped like spiky ovals or bricks with rounded corners.
A virus uses the metabolism of its host cell for its reproductive needs. Viruses need no nutrition themselves, as they are not living organisms.
Examples: The Small Pox Virus, Rhino Virus (Common cold), and HIV virus (AIDs).
Good: Can benefit from viruses in gene therapy
Bad:Some are very deadly and spread through fluids (ebola, marburg)