biological weapons

iv’e heard a bit about biological weapons in the past and some seem nasty and some seem really nasty. does anyone know any background on them and if so what are they? it seems to me like decendants or mutations of the influenza virus would probably be very nasty. what others?

FAS Fact Sheets on Chemical & Biological Weapons

In addition to those the above link, smallpox is also suspected to be a weapon in bioterror.