Virons do not grow. They have no nucleus, cytoplasm, or membranes. They do not carry out cellular functions. Virons do not generate metabolic energy. They are obligate intracellular parasites, meaning that they require a host cell to reproduce.
Viruses can be harmful.
Virulent - disease causing. Temperate - not immediately disease causing. Viruses play a role in causing some cancers. Viruses may be helpful. A temperate virus introduces nucleic acid from its former host into a new host, thus changing the genetic code of the host.