How can a virus infect another virus?

Answer 1

A virus that infects another virus is referred to as a 'virophage', and are often referred to as satellite viruses (catch the reference?). These viruses rely on co-infection of the host cell with larger virus so that they can essentially hijack their machinery for replication, translation, etc. A good example of a virophage is the Sputnik virophage, which lives in amoebas that are also infected with a Mimivirus.