Is your computer vulnerable to a virus?

I've received several queries recently from readers who have heard or read news stories about a "computer virus" that reportedly can attack a computer and destroy stored programs or data. People want to know whether such stories are true -- and if they are, how to fend off a viral attack.

"Computer virus" may sound like something out of a sci-fi movie on the Late, Late Show -- a future civilization, dependent on robots and computers, faces disaster because its machines have mysteriously gone on the fritz.

In fact, computer virus refers to a kind of software program that can work its way through the memory or hard disk of a computer and alter or erase stored files.

There really is a computer virus -- produced by computer tekkies who feel a need to flex their programming muscle in harmful ways. The good news is that such programs are rarely a threat in the personal computer world. And they are fairly easy to defend against.

The best-known recent case of a computer virus attack was the widely reported problem within IBM Corp.'s internal office network last December. Someone -- corporate officials say they've traced the source to West Germany -- sent in a "Christmas card" program to an IBM employee via the IBM electronic mail network.

On the screen, this electronic Christmas card looked innocent. It displayed a Christams tree and a message of good cheer. But the programmer who wrote this "message" was clearly familiar with IBM's electronic mail network. For the program knew how to burrow into each employee's automatic routing slip data base. Then it would send a copy of itself to each work station on the route. Each time the program landed, it would start sending itself out again.

The result was an explosion of traffic in the electronic mail system that might have brought all network messages to a halt, if IBM hadn't caught the offending program and dispatched it to electronic oblivion.

The trade journal Computers and Security reports in its February issue about a somewhat similar virus that was sent to the National Aeronautics and Space Administration's Space Physics Analysis Network, a big data base of information available to users worldwide. NASA, too, evidently cured the problem before much was done.

These cases involved networks of work stations or even bigger computers. That's the first key point to recognize about the computer virus reports -- they don't involve personal computers. But there have been stories -- none substantiated, to our knowledge -- of virus programs floating around the PC world as well.

In the message areas of some arcane bulletin board systems, we've seen hackers exchanging tales of alleged "worm" programs.

The story goes that you download one of these worms from Compuserve or a user-group bulletin board, and it starts burrowing through your hard disk, making all your files unreadable.

There have been rumors over the years about copy-protection schemes that will dispatch a worm into your hard disk if you try to copy the master disk illegally. If there are any actual cases of this stuff happening, I'm not aware of them.

The common thread in all these cases is that the virus had to be introduced into a computer (or network) from the outside -- either through a message sent via electronic mail or a downloaded file.

If you never "feed" your machine anything but programs from established software houses, your machine will be immune.

If you like to call up bulletin boards to download programs, or exchange messages via electronic mail systems, then there is a chance that your hard disk could be infected by a virus program.

The possibility is so unlikely that you really needn't worry much. But if you're worried, here are a couple of antiviral prescriptions.

First, you can easily set up a simple "security guard" on your computer, so nobody can send you a message or program without entering a password. Most major communications programs -- SmartCom, CrossTalk, Mirror, etc. -- have password functions you can implement.

There are also programs around -- Borland's SuperKey is a good example -- that let you set up a password system for anyone who tries to boot up your computer. That will protect you from unauthorized use by other people in your office.

The second defense against a computer virus is to back up your hard disk regularly onto tapes or floppy disk. Then, in the unlikely event that a virus messes up your hard disk, you'll have the files and programs in back-up form.

In sum, my answer to personal computer users concerned about computer virus is: Don't worry.