From a pair of computer industry reporters (Markoff: The New York Times; Hafner: formerly with Business Week)--three cautionary tales of 1980's computer hackers gone amok in this dark-side correlate to Steven Levy's more optimistic Hackers (1984). They lived thousands of miles from one another--Kevin Mitnick in Los Angeles, Pengo in West Berlin, and Robert Morris in Ithaca, N.Y.--and their personalities were widely divergent, but in the no- man's land of international, complexly interlinked computer networks these three hackers not only shared an addiction to computer intrigue but probably encountered one another prowling through secret computer files along the way. Mitnick, an overweight, unemployed high-school dropout, began ``phone phreaking'' and computer hacking to tap phones and meddle with his enemies' credit ratings until he managed to break into the secret electronic research files of a leading computer manufacturer. Pengo, a West German teen-ager who enjoyed ``traveling the world'' via computer networks and considered penetrating the files of Darpanet, the US defense network--an irresistible challenge--found himself drawn into Project Equalizer, a bumbling youthful effort to sell computer information to the Soviets to further world peace. Robert Morris, an introverted Cornell Univ. computer-science graduate student and son of a National Security Agency computer- security expert, mischievously planted a supposedly harmless ``virus'' in a computer network and accidentally shut down Darpanet and other networks across the country. Sentences for all three electronic wanderers were surprisingly light--a fact that apparently irritates the authors, who claim that hacking, spawned by the philosophy that all information should be freely shared, has long since been transformed into a threat to security that should be punished more severely in the future. Disturbing tales for would-be computer outlaws as well as those who fear them.