There are two general ways in which viruses may be classified. One is the classical monothetic hierarchical system applied by Linnaeus to plants and animals. This is a logical system in which divisions are made as to the relative importance of different properties which are then used to place a taxon in a particular phylum, order, family, genus, etc. Adanson (1763) proposed the classification of viruses.
1. Animal Virus: These viruses infect by invading the cells of animals, including humans.
Example: Influenza, mumps, rabies, polio virus, etc.
2. Plant Virus: These viruses infect plants by invading the plant cells. Replication of plant viruses is obligate and does not happen without a host.
Example: potato virus, tobacco mosaic virus (TMV), cauliflower mosaic virus, etc.
3. Bacteriophage: Bacteriophages are found in nature wherever bacteria occur. They are especially found in abundance in the intestines of man and other animals. There are many varieties of bacteriophages, such as DNA viruses, RNA viruses, λ page, etc.