Some viruses take use a cell to make more viruses and in the process kills off the cell. Other viruses will actually take over the cell and reside in the cell and live there but becomes active at certain times. Viruses Viruses are difficult to classify. They do not have many of the properties of cells.
Viruses have no cell membrane.
Viruses have DNA but they must inject it into another living cell to cause it to produce more viruses.