BOOK REVIEW : Twice-Told Tales of Computer Mischief : APPROACHING ZERO: The Extraordinary Underworld of Hackers, Phreakers, Virus Writers and Keyboard Criminals <i> by Paul Mungo and Bryan Clough</i> ; Random House $22, 247 pages

Among the many consequences of the personal computer over the last dozen years has been a staggering growth in computer crime, made easier by the proliferation of terminals at home.

Included in this category is illegal hacking--using a computer and a telephone line to break into remote mainframes for mischief or malfeasance, usually the work of young men motivated by a desire to beat the system and show that it can be done.

From time to time, the computer underground has made it into the news, by cracking into and wandering around the computers of NASA and NORAD or by setting loose a computer virus that crippled the Internet, a network of computer networks.

More often, these computer capers have been played out less conspicuously, though they have captured the continuing attention of law-enforcement agencies around the world.

Paul Mungo and Bryan Clough flesh out many details of computer crime and computer criminals in “Approaching Zero,” a book that argues that no electronic information held by banks, universities or government agencies is safe.

Mungo, a science writer, and Clough, a British expert on computer security who advises New Scotland Yard, provide details of how various computer crimes have been carried out and offer descriptions of the perpetrators.

“That some young men find computing a substitute for sexual activity is probably incontrovertible,” the authors assert--without any supporting evidence.

Despite such spicy claims, the book is somehow flat. It’s not as if this is the first time these stories have been told. Some are new but many are familiar, and the overall effect is decidedly old hat.

Clifford Stoll gave chapter and verse of one hacker’s activities in “The Cuckoo’s Egg” (Doubleday, 1989); Steven Levy covered the landscape in “Hackers” (Doubleday, 1984), and Katie Hafner and John Markoff provided an excellent description in “Cyberpunk” (Simon & Schuster, 1991).

Although there are other hackers and new stories--including much about computer viruses in Bulgaria, of all places--there does not seem to be enough that’s new to justify another book.

To be sure, Mungo and Clough add interesting details and observations. They argue that computer viruses were over-hyped for years before their threat became as serious as the hypists would have you believe.

They assert that this hyping was largely the work of people trying to sell anti-virus software.

But eventually, they concede, dire warnings about viruses came true. After spending many pages deriding the prophets of doom, Mungo and Clough eventually join the bandwagon.

“As the world population of computer viruses grows exponentially,” they say, “so does the potential for real disaster. . . . A virus let loose in a hospital computer could harm vital records and might result in patients receiving the wrong dosages of medicine; workers could suffer job losses in virus-ravaged businesses; dangerous emissions could be released from nuclear power plants if the controlling computers were compromises and so on.”

They also make a factual error about public knowledge of computer viruses, asserting that the first press report on the subject probably appeared in February, 1987, in the magazine Computers & Security. In fact, Discover magazine published a long report on computer viruses in November, 1984.

Mungo and Clough have adopted an annoying practice of recounting long, detailed stories of various computer crimes and then ending by saying that the alleged victim of the alleged crime denies that it ever took place.

For example, they say that the breakdown of the AT&T; long-distance system in January, 1990, could have been caused by a computer bomb planted in the system, and they describe how that could have occurred.

They note that AT&T; had received a threat of a computer bomb a short time before.

But after telling the story, they say, “There is absolutely no proof that it was a computer bomb, and AT&T;’s final, official explanation remains that the shutdown was caused by an errant piece of software.”

Then there is a long story about two young hackers who used a complicated scheme and a Swiss bank account to filch more than $130,000 from Citibank.

After recounting this tale, the authors write, “You can believe this story or not, as you wish. Certainly Citibank doesn’t believe a word of it; it has consistently denied that anything resembling the events described above have ever happened. . . .”

But you should never let the facts get in the way of a good story.