It has been argued that the smaller viruses associated with giant DNA viruses are a new biological entity. However, a short article in Nature Reviews Microbiology argues that these smaller viruses should be classified with the satellite viruses (which I tend to agree with).
Virophages or satellite viruses? Nature Reviews Microbiology 9, 762-763 (November 2011) | doi:10.1038/nrmicro2676
Studies on the giant DNA viruses Acanthamoeba polyphaga mimivirus (APMV) and Cafeteria roenbergensis virus (CroV) have revealed that much smaller viruses – Sputnik and Mavirus, respectively – are associated with them. These smaller viruses depend on the giant viruses for propagation, although the giant viruses can grow without the smaller viruses. It has been argued that Sputnik represents a new, previously unknown biological entity: a ‘virophage’. This term is now used by an increasing number of researchers. However, the virophage concept and its status as a new biological entity requires objective assessment of the similarities and differences between the virophages and the ‘classical’ satellite viruses that have been described previously.