THE HACKER WHO VANISHED Suicide or clever hoax? Early one morning last September, a pair of California computer whizzes were doing what hackers like to do best: peering at a glowing terminal, hacking away at a programs and talking about the books and movies they might someday write about their electronic exploits. Tom Anderson, 16, paused to take a shower. "When I came out," recalls Anderson, who had left his friend, Bill Landreth, busily pounding away at the keyboard, "he was gone. And I haven't seen him since." Landreth's disappearance from Escondido, a suburb of San diego, is of concern to more than his family and friends. Three years ago, Landreth-- whose IQ measured 163 and who was only 19 at the time--was convicted of wire fraud after he tapped into a GTE electronic-mail service whose clients included NASA and the Defense Department. Landreth passed the access code along to other hackers; soon computer users around the country were using the GTE lines for free. But since Landreth (known to other hackers as "THE CRACKER" from the book INNER CIRCLE) hadn't altered any message or stolen any money, the judge let him off with three years' probation. Landreth later capitalized on his notoriety by writing a book about breaking through computer security screens and by advising businesses on how to protect their system against the type of intrusion that got him in trouble. But by disappearing, Landreth broke his probation terms and is now being sought by U.S. marshals. The hacker's friends doubt that he is on the lam. "It's not unusual for him to disappear," says Jenny Perkes, a former girlfriend. Indeed Anderson remembers that Landreth liked to cultivate an air of mystery and recently had taken off to Mexico and later Sweden without telling anyone, returning a week later as if he had just been to the corner store. But Landreth has never before been gone for such a long period; and this time he vanished without leaving money for rent--a discourtesy that friends say is totally out of character. "He was a gentleman, a very thoughtful person, very generous,"says Perkes. Landreth left something esle behind, however: a rambling eight-page letter that only added to the mystery. Landreth apparently wrote the letter, which was addressed to no one and left in his room, during a period last summer when friends say he appeared depressed. The rambling discourse touches on such topics as evolution, nuclear war, society's greed, computers becoming more important than man,the meaning of existence and, ulitmately, suicide. "The idea is that I will commit suicde sometime around my 22nd birthday ," the note said. "This will have given me 22 or so years with which to convince myself that life really isn't worth living." Landreth's 22nd birthday was Dec. 26. Anderson, for one expects never to hear from his friend again. Cryptic message: But Landreth's apparent suicide note had an escape clause. Some months after typing the suicide reference, he added the words: "Since writing the above, my plans have changed slightly. I am going to take this money I have left...and make a final attempt at making life worthy. It will be a short attempt, and I do suspect that if it works out that none of my friends will know me then. If it dosen't work out, the news of my death will probably get around (I won't try to hide it)." Does Landreth's note reflect a troubled youth contemplating suicide or an adventure-loving computer genius playing an elaborate real-life Dungeons & Dragons like game on his friends? So far, neither the police nor the federal marshals nor his friends have been able to crack the mystery of the hacker who one day disappeared leaving no trace than a computer deleted sentence. George Hackett with Hilliard Harper in San Diego