A virus is a parasitic organism that cannot replicate on its own. A virus, on the other hand, can command the cell machinery to make new viruses once it has infected a susceptible cell. The genetic substance of most viruses is either RNA or DNA. Single-stranded or double-stranded nucleic acids are both possible. The nucleic acid and a protein outer shell make up the entire infectious virus particle, known as a virion. Only enough RNA or DNA is present in the smallest viruses to encode four proteins. The most complicated genes can encode between 100 and 200 proteins. Infectious pathogens are responsible for around a fifth of all human malignancies globally. Seven distinct viruses have been causally related to human oncogenesis in 12% of cancers.