The era of the information thief has arrived and with it a lucrative market in devices and software designed to keep the hacker at bay.

But none of these anti-theft measures will work, said computer security specialist Jeffrey Kennedy, unless they're installed and used."If you're going to do it, keep it simple," he said.

Among the simplest of items that can be installed on a personal computer is a data encryption system that operates separately from the word processing, data processing or spreadsheet software most often used on a particular machine.

Simply put, encryption software takes information already stored on magnetic media, scrambles it and puts it back on the disk.

The program, of course, allows the information to be unscrambled by the user with the right code.

"The trouble with a lot of the encryption schemes out there is they are cumbersome. They take a lot of time. Some are very RAM (random access memory) intensive," said Kennedy, meaning they use quite a bit of available memory that might be better allocated to other functions.

There's also the problem with data interaction. "Most of them won't interact with WordStar or Word Perfect, (two of the most popular word-processing programs)," said Kennedy.

The encryption program resides in the same memory area of the computer as the program, which can mean both will malfunction in the event of data interaction.

"And, of course, no security system works if you don't use it," he said.

The cost for such a system ranges from the type of software available for a nominal sum to about $100 for a sophisticated encryption program like "SuperKey," produced by Borlan.

With encryption, the information on the disk is safe.

At least, it's safe from the casual hacker if the computer is not accessable via telephone lines and a modem.

But a sophisticated computer criminal might, if the information is interesting enough, make a greater effort to get to it. And if someone knowledgeable enough wants the data on a disk that's accessable to a modem, there's a good chance the hacker will get it.

Unless it's encrypted. Then the information is available only to people who know the code word to unscramble the data.

The problem with code words is that "once again a human factor has to be figured in," said Kennedy. People tend to forget or lose code words.

His company, Anchor Pad International in Ventura, Calif., makes a combination software-hardware security system for personal and small business computers that is almost as simple to use as turning a key.

A big, red lock fits on the primary disk drive of the personal computer. It keeps the Anchor Pad Plus software program inside the drive. It cannot be removed unless the key is inserted, turned, and the lock is removed.

But this system deals again with a "human factor" - the key, which can be lost.

IBM's AT and a number of IBM clones have a lock on the central processing unit case that shuts off the keyboard when it is turned off.

"They're effective, but they don't get used on a regular basis," said Kennedy. "People don't take time to turn the key when they leave. Most people don't even know where the key is. I have a PC, and I don't."

The Anchor Pad Plus puts a big red lock on a computer system's "A" drive, allowing the computer to be turned on and booted up without a key. The user is then able to start the system and get into the computer's hard disk upon entering a correct code word.

Another aspect of Anchor Pad is the fact that if someone walks away from an operating terminal, the software begins counting down.

"After a user-defined period, ranging from five minutes to half an hour, a security screen pops up," he said.

That screen covers up any sensitive information that might be left on the screen. It can be disabled by entering the code that allows access to the computer in the first place.

This brings the "human factor" into play again. The user has to know the code to get to the information.

Like keys, code words have a way of getting forgotten.