APPROACHING ZERO: Data Crime and the Computer Underworld By Bryan Clough and Paul Mungo (Faber, $70) ONE of the earliest signs that the electronic age faced serious danger from unexpected quarters came after a chance discovery by an eight-year-old blind boy called Joe. Joe Engressia loved the telephone, because it was a way for a sightless child to reach out. One day, Joe noticed that when he whistled while listening to a taped message, the tape would stop. The technical reason - something Joe would find out later - was that he had accidentally whistled a 2,600-cycle tone. This, in the language of telephone computers, said that the call was terminated. The computer stopped charging for the call, but the connection remained in place. The rest of the call became free. Joe and other blind youngsters soon learned to manipulate the international telephone system by reproducing the sounds that controlled the telephone company's electronic hardware. They used whistles. They used the gaps between their teeth. They held Hammond organs next to the handset. They gave themselves calls to any part of the direct-dial world, all free of charge. This happened in the late 1950s and early 1960s, and the young people using this system were called phreakers. But as the world of computing developed in the following decade, phreaking evolved into hacking, and eventually the growth of the ''cyberpunk''generation, addicted to the world of electronic impulses. It really was the revenge of the nerds. Bright young kids (almost always male) could sit in their bedrooms playing with home computers. Playing video games? Sort of. Actually junior was transferring money from global banks into his savings account. Or manipulating factory computers to send him free samples. Most of us think of computer viruses as inconvenient tricks that cause us to get our computers checked on March 6 every year. But they can be far more deadly. In 1989 and 1990, thousands of computer users received a free floppy disk in the mail. It claimed to be a databank of AIDS information. But it was also the nastiest piece of computer blackmail on record. A secondary program on the disk would stay hidden for most of the year. Then, if the recipient failed to send a large amount of money to a post office box in Panama, the computer would develop ''computer AIDS''. An electronic virus would destroy all the data in its hard disk and infect every other disk it came into contact with. How the AIDS blackmailer was caught, and dozens of other amazing-but-true stories of the electronic age, are contained in Approaching Zero. This is one of the best-written books on data crime. It is genuine reportage, with the points being illustrated with detailed case histories. Names are named, and dates and times are given. Yet the stories are told in a simple enough way to be understoodby non-computer-literate people. And despite the fact that much of this book tells the story of people who damage the establishment and cause losses to ''innocent'' companies, it is surprisingly uplifting. This is because the perpetrators of the crimes start with so little equipment - usually a children's home computer and a telephone - and yet manage to spend their time tip-toeing through the secret memory files of the most powerful people on this planet,including those of the president of the United States. This is human resourcefulness at its best.