Which is older: 'virus' or 'archaea'?
There is an assumption based on Darwinian evolution that the simpler the organism the older it is. Based on this assumption it would be logical to belief that virus are older than archaea
However virus can not exist on their own they are dependent on other organism to replicate their DNA or RNA. Therefore another organism must have existed before virus for the virus to live off.
All observable changes in living things actually show a chance form the complex to the simple. It is reasonable to assume that the virus is a evolutionary change from a more complex organism, becoming what it is now a parasite.