What property of a virus makes it useful for making transgenic organisms?

Viruses reproduce by incorporating their DNA into an organism's genome to tap into the host replication mechanism to reproduce themselves. Viruses, therefore, cannot copy outside their host. This property of viruses makes them suitable for the production of transgenic organisms. This is achieved by replacing the DNA piece that causes virulence in the virus with the desired gene that is to be transduced into the host organisms.