Two years ago, the Department of Homeland Security stepped up its campaign to install controversial body scanners at airports nationwide. At the time, the agency claimed the machines could spot all sorts of hidden weapons and contraband. Today, more than 700 of the imagers are in place at 180 airports. But the so-called “naked” scanners may not be quite as all-seeing as they were originally billed to be. Quietly, DHS has called in the Pentagon’s premier research agency to help develop a new generation of imagers that are faster, smaller, more precise, and less prone to hacking.