Is a dust mask rated N95 protect against harmful viruses such as bird flu, etc.?

MSA (Affinity) FR211 dust maskIs a dust mask rated N95 protect against harmful viruses such as bird flu, etc.?
N95 is one of many classifications of mask (that also include n99-n100, r-95/99/100, and p95/99/100. Actually, 99, I've only seen for N. But anyhow, N means non-oil based particles, R means resistant to oil and other particles, and P means oil and particulate proof. So, N95 is plenty adequate (but not the best), and often used in the medical field (often the bright bluish-green 3M model 1860).Is a dust mask rated N95 protect against harmful viruses such as bird flu, etc.?
It is supposed to be the one for protecting against airborne viruses.