Scientists in France have discovered a virus infected with a second virus in a cooling tower. Based on the sequencing of the infecting virus's genetic code researchers believe there might be an entire class of viruses that infect other viruses.
Normally viruses can only be seen in an electron microscope. The infected virus was a large mimivirus, a class of viruses large enough to be seen in an optical microscope. The infecting virus has been named 'Sputnik'
The discovery is likely to reopen the debate over whether viruses should be considered to be living organisms. Traditionally they haven't been because they cannot metabolise food and do not have their own cellular structure.