Working from a beige house at the end of a dirt road, Jeff Bardin switches on a laptop, boots up a program that obscures his location, and pecks in a passkey to an Internet forum run by an Iraqi branch of al-Qaida. Soon the screen displays battle flags and AK-47 rifles, plus palm-lined beaches to conjure up a martyr's paradise. "I do believe we are in," says Bardin, a stout, 54-year-old computer security consultant. Barefoot in his bedroom, Bardin pretends to be a 20-something Canadian who wants to train in a militant camp in Pakistan. With a few keystrokes, he...