1.They are acellular, that is, they contain no cytoplasm or cellular organelles.
2.They carry out no metabolism on their own and must replicate using the host cell's metabolic machinery. In other words, viruses don't grow and divide. Instead, new viral components are synthesized and assembled within the infected host cell.
3.The vast majority of viruses possess either DNA or RNA but not both.
4. Based on the large number of protein folds encoded by viral genomes that are shared with the genomes of cells, which this indicates that viruses likely arose from multiple ancient cells.