It is defined as an unguided and proliferative growth of cells which form tumor and invade other body systems. Some viral genes (herpes virus, papilloma virus, epsteinn barr virus and hepatitis B virus) also play an important role in occurrence of cancer. Some of their modifications are known as proto or cellular oncogenes. There are some interesting types of genes known as Jumping Genes. These genes actively change from proto to cellular and vice versa.
Viruses are a link between living and non living entities. As their feature overlaps both the living as well as non living characters. So till date it is very hard to put viruses into either of this category. For example, as they do not respire, have no energy storing system, no growth and depend on other living organisms for their survival but they can reproduce, can cause infection, and can breed are ultra violet x ray sensitive. They are basically product of nucleoprotein material.