Virophage is the name coined for viruses such as Sputnik and Mavirus that can only replicate in cells infected with a helper virus, whose replication they inhibit. I’ve never liked the name – it means virus eater – and neither does Brent Johnson, a virologist at Brigham Young University:
“I believe the term ‘virophage’ is unfortunate because it implies one virus is infecting another virus and eating it. The small virus isn’t infecting another virus, it’s just using it to assist in replication, which is consistent with the needs of a defective virus.” he explains. He prefers calling the giant viruses “megaviruses,” and considers the name “Megavirus-Associated Virus (MAV) more consistent with currently accepted virus nomenclature.”
For more discussion, see the article by Marsha Stone in the July 2011 Microbe.