Charles Epstein was sitting at the kitchen table when his daughter Joanna brought in the padded brown envelope with the day's mail. He saw nothing unusual about the package, but when Epstein, a geneticist at the University of California, San Francisco, opened the package, it exploded. Rushed to the hospital, Epstein lost several fingers on his right hand, broke an arm and suffered severe abdominal injuries.
Two days later, David Gelernter, an associate professor of computer science at Yale, received a package at his office in the college's computer-science center. It blew up in his hands. Wounded in the abdomen, chest,...