Technology: A Bold Raid on Computer Security

For months the computer intruder moved like an invisible man -- until one day Clifford Stoll saw the footprints. The frizzy-haired Stoll, 37, a systems manager at California's Lawrence Berkeley Laboratory, knew something was amiss when one of the computers in his care revealed that an electronic trespasser was trying to use the lab's machines without providing a billing address. Suspecting the intruder might be a student prankster from the nearby University of California campus, Stoll launched a novel experiment. Instead of shutting out the interloper, he allowed him to roam at will through the system while carefully recording his every...