The cargo container-that ubiquitous truck-sized box that carries goods around the world-could be the ultimate poor man's missile. Each year more than 48 million loaded cargo containers move between the world's seaports. But of the six million that arrive in the U.S., only 5 percent have their contents visually inspected or x-rayed, opening the possibility that terrorists could use them to smuggle in nuclear material, explosives, or even themselves. Many of the world's ports are joining a U.S.-led effort to manually inspect containers considered high risk; but at the same time, a host of technologies are being readied to plug this security hole.

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