We usually deal in facts and try to disprove the fiction spread by some computer peddlers. Today we're going to focus on fiction. We read a novel that ought to go on your must read list.

"Mismatch" is a first novel from Lloyd Pye. This entertaining $4 Dell paperback offers more insight into the near-criminal weaknesses in our nation's computer and telephone links than we've seen in any non-fiction work to date.It's also a guided tour for anyone who's never ventured into the technologically wild and woolly world of computer hackers and their close kin, the phreakers. If you own a computer system that's connected to a phone line, it's a tour we urge you to take.

A phreaker (corrupted from `phone freaker') is someone who understands telephone technology so well that she can get through many of a phone system's fiscal safeguards. For instance, a phreaker can dial up someone in Moscow, Idaho, or Moscow, Soviet Union, without spending a dime.

Phreakers were around long before Pye wrote this book. One of the first and still best known of them went by the name of Cap'n Crunch until he was caught. Now out of his teens, he was among Pye's technical consultants for the novel. Others included some retired Naval security officers.

The premise of Pye's fiction is one some people will hurrah: That the dismantling of monolithic Ma Bell was one of this country's most bizarre and apparently pointless government decrees.

Remember the world-famous efficiency of this, our most fundamental system of information transferral? In a time of otherwise rapid technological advance, it was replaced by a proliferating plethora of phone servicers. The result: mass confusion and heavy-handed ineptitude.

So why was it done? To keep the United States safe from phreakers, Pye's book says.

The major protagonist is a former phreaker who got caught. He's serving his time by being a Ma Bell counter-phreaker. His best girl is a crack investigative reporter for a Silicon Valley newspaper.

Other major characters on the side of truth and justice include a few hard-working National Security Agency functionaries and some Naval officers of mixed pedigree.

On the other team are two Soviet spies.

That's plot number one. Plot number two involves two incredibly dumb FBI agents and a hacker.

Time for another aside, this one on hackers. The word often raises hackles, for no good reason. Few hackers do anything illegal.

Hackers do share three things in common. One, they love the power in computers. Two, they are very, very good at tapping that power. Three, they're ready to take on any challenger who sets up a computer system that's supposed to be off-limits and then invites the world in.

Pye's tale has the two FBI men finally nailing a famous hacker named Ghost Glitch after years of investigation. While the hacker did do some mischief by invading unsecured computer systems, he hasn't broken enough of a law to keep him in prison. The frustrated lawmen take preventive justice into their own hands. They rough him up.

The hacker gets mad. He decides to really cause some grief. He decides to shut down all the networks of computer and telephone connections throughout the entire United States for just long enough to make his point. Glitch has the brains and the hardware to make good his threat. He understands hacking better than the FBI understands how to stop it.

Stop right there! Pye's plot is fiction. But his premise is not so far from reality. Right this instant, we could name several hackers who could conceivably pull the same switches.

Here's what would happen: All phone calls would stop dead. All phone-line computer networks would stop transmitting. Credit card sales would cease. Many radio and TV stations would go off the air.

In some cities, traffic lights wouldn't work. Burglar alarms would quit.

Happily, the hackers we know are law-abiding. More happily, most of them are sensitive, caring people.

But there are some who aren't. If you think your computer - or your government's - is safe, read the book.

Then stay tuned here. We'll tell you in future columns how you can secure your system from unwanted entry. We'll also tell why most so-called computer security gadgets are practically worthless.