What are viruses and their good and bad properties?

Viruses are a specific form of life. They can live only in alien organisms, more precisely in their cells, since they do not have their own). Viruses are known as carriers of all kinds of diseases, some of which are deadly and very difficult for the body to cause an epidemic. Viruses also have useful applications for humans: they are used in vaccinations to increase immunity, they are also fed and used in genetic engineering.