Not necessarily true. Smallpox is normally spread through aerosolized virus pariticles which are inhaled. An old method of innoculation called variolination exposed previously unexposed people to the variola (smallpox) virus via an incision on the skin. The patient would then get a milder form of the disease but would become infectious to others. This method of innoculation which had a 1% fatatity rate, was used on George Washington when he was a young man and by the Continental Army during the American Revolution. If terrorists used variolination, they could easily spread smallpox while not being terribly sick themselves or facing a high risk of death.