What is virus? Virus is a small parasite and usually refers to particles that infect eukaryotes and can’t reproduce by itself. Because the very small size of the virus can only be seen using an electron microscope with a size of 0.025 millimicron-0.25 millimicron. One of the inventors of the Russian botanist in 1982 named Dimitri Ivanowsky. Dimitri conducted an experiment by filtering the sap from diseased tobacco using a bacteria-specific sieve. The origin of healthy plants is ultimately contagious. As for the characteristics of the virus is a follows :Doesn’t have cellsIs a parasiticCarry out metabolic activitiesHas a very small size that is about 20-300 millimicronThe virus has only one nucleic acid, DNA or RNABody shape variesIt can only reproduce in the bodies of living thingsBesides that as for the types of virus is a follows :HIV HIV belongs to one of the retro virus, which specifically attacks the white blood cell, the virus has an enzyme that is a transcriptase enzyme that converts a single ARN chain into a double chains of copies of ADN.Influenza virusInfluenza virus, replica of influenza virus is almost the same as the herpes virus replica cycle only in this virus genetic material in the form of a single chain ARN, which then undergoes a replica into mARN.Paramyxo virusParamyxo virus is a kind of ARN virus which subsequently undergoes replica to be mARN.The advantages of virus is virus are used for vaccine production. For example sabin vaccine to prevent polio, TBC vaccine, typhoid fever vaccine. Virus can be used as insulin material. For example cancer-causing virus that can be transplanted with the producer of insulin or other substances into bacteria so that the bacteria can breed quickly and simultaneously produce insulin and other substances. Virus can be used as gene therapy which can alter the infecting genes into healing genes.The disadvantages of virus is :(a). Causing various diseases in humans : HIV is a very dangerous virus that attacks the human immune system, bird flu is a virus that is transmitted by birds to humans and is very dangerous and dengue fever is a virus that is spread by aedes aegepty mosquito to humans. (b). Causing various diseases in plant : TMV or mosaic disease in tobacco plants and tungro is a disease that causes rice plants to be dwarfed and damaged. The cause of this virus is done by planthopper pests. (c). causing various diseases in animals : Tetelo diseases that attacks the poultry, especially chickens, nail and mouth diseases that attacks cattle and buffalo, and cancer diseases in chickens by RSV (rous sarcoma virus).Solution to prevent virus is drink plenty of clean water, increase consumption of vitamins derived from vegetables and fruits, maintain a healthy lifestyle and consult a physician or see a doctor to check the condition of the body.