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.