They are not alive.
They are nonliving.
They are like cockle burrs that "grab" hold of your clothing or a dog's coat. They are hijackers. Once they get attached to the cell of a living cell, they can take it over and "make" the living cell produce virus particles instead of cell parts. These parts can assemble into more viruses and then they break out of the cell (killing it) and begin the process again. They cannot make more viruses on their own.