Considering viruses complete their life cycle by hijacking your own cellular machinery and using it for their own benefit, and considering the fact that if a cell recognizes it is infected with a virus it will sucide (assuming the infected cell isn't killed by your immune system first), and also considering that infected cells can have up to 1 million viral particles inside them, oh yeah and also considering the fact that for some virsues the only way they can get out of the cell after assmbly is by blowing it up, what exactly is a 'harmless' virus?
Also viri isn't a word pertaining to multiple virus particles - its viruses.
A few cool facts-
One of the microbes used to make yogourt is also present as part of the normal flora of the human vagina.
Bacteria and other intestinal microbes may consititue up to 50% of the mass of fecal material.