I think the cases of "norwalk" virus on the cruise ships is a demonstration of how easily a smallpox attack could be accomplished. The spread of West Nile is also an example of how simple it is to introduce a vector borne virus. These are simple "probes" to test the perimeter. There isn't one. A release of a weaponized bioweapon is unlikely to be detected or halted until well after a significant deployment. It won't be a very nice situation.
I think that Saddam has already secreted plenty of anthrax or smallpox in the USA, and his "failsafe firing system" is providing the address of the mini storage garages or similar where they are hidden to Al Qaeda.