Box cutters, some flight training and a lot of determination. Although it now seems clear that the hijackers of September 11 had the support of an international terror organization, the real lesson is that it is frighteningly easy for a small number of intelligent people, acting together, to do a tremendous amount of damage.

Technologists routinely underestimate the power of lowtech attacks. After all, it's much more interesting (and lucrative) to work on the Bush administration's national missile defense project than to think up practical strategies for protecting office buildings from fire, truck bombs and suicide pilots.