Viruses are infectious agents that survive only inside the living cells (host body), they need a host for replication and can have either DNA or RNA as the genetic material which replicates. These microorganisms do not have their energy and are therefore known as obligate parasites that use the energy of the host for its survival. The virus has either DNA or RNA as genetic material but never both together. All viruses contain protein. Only enveloped viruses are susceptible to lipid solvents.