Eubacteria and Archaeobacteria are procaryotes. Procaryotes lack nuclei. Procaryotes are unicellular, although the cells may grow in organized and connected groups. All procaryotes are bacteria.
Eucaryotes have nuclei and other membrane-bounded organelles.
Viruses are not classified in the tree of life. Virus consist of DNA or RNA enclosed within a protein coat. Sometimes there is also a lipid bilayer around the coat. Viruses can not replicate outside of a living cell. They are obligate parasites.