New Year Brings Batch of Devious Computer Viruses.

JUST over the past few months, several new types of computer viruses have appeared that break mischievous new ground.

They can strike at pretty much any time, and they are sometimes designed with deliberate harm in mind.

It used to be that the biggest threat of infection to computers was the floppy disk. Before the Net came into widespread use, transmitting a computer virus usually required some kind of active involvement on your part. Most often, that meant putting an infected disk in your computer.

Then came e-mail, which made it possible for people to mail viruses to you instead of waiting for a chance to stow away on a floppy. And even worse, viruses can now mail themselves to you.

This dramatically increased the contagiousness of computer viruses, but they were still generally limited to e-mail attachments. You'd get some unknown file in the mail, open it up to find out what it was, and that would be enough to activate the virus inside.

Now, in this brave new world, truly malicious viruses can start to work on your computer without your needing to do much of anything to help them along. The very act of trying to determine what they are and delete them can bring them to life.

Devious tactics

For example, a virus that appeared in November made a remarkable technical achievement. All that it needed to be activated was for you to highlight the subject line of the e-mail message it came in. The virus would then mail copies of itself to people in your address book.

This virus, known as BubbleBoy, only affected Microsoft Outlook and Outlook Express e-mail clients running under some configurations of Windows. The security breach was also relatively easy to close and didn't do much harm. Nonetheless, this virus may have been the first of many that will work in similar ways.

Yet another new virus called Babylonia appeared in early December and achieved another infectious milestone. Babylonia, which circulated in Internet chat rooms as an offer to fix the Y2K problem, is the first virus that can mutate under the control of its creator. The virus hides itself on your computer, waits for an open Internet connection, and then checks with a Web server to update itself and deliver a range of more destructive options. It can also change form to elude detection.

Even more viruses may be waiting for the Year 2000, when they might first be diagnosed as Y2K-related trouble even while they are spreading more widely.

Most simply, you can be more careful about the e-mail you open. I don't know about you, but I get about 20 junk-mail messages a day by e-mail. Usually the junk is easy to spot since the subject line makes misspelled promises of money, fame and the fulfillment of my wildest fantasies.

That's all very appealing, but it's best to treat these messages -- and especially the attachments they may contain -- the same way you might treat someone who came to the door in a clown wig saying he was there to read the meter.

Scrutinize attachments

Depending on the e-mail application you use, you may be able to set up filters that screen out at least some of your junk mail.

Given the risk of viral attachments, it's also good netiquette to tell people about any attachments you're sending to them. That may help prevent your document from being viewed suspiciously by its recipient.

My own e-mail program, for instance, is set up to put all attachments in a specific folder. Sometimes when I'm looking for something that I know someone has attached for me, I find all sorts of mystery attachments too. They go straight to the trash.

Maybe because Microsoft's software is so widely used -- but also because of certain built-in capabilities -- many viruses affect only Microsoft applications running on the Windows operating system. Microsoft Word, for instance, is a popular target. See www.microsoft.com/security for information and the latest security patches.

It's also important to remember that just because a solution exists for a particular virus doesn't mean that you are protected. Some computer viruses that can be "cured" are nonetheless still out there, and they can still damage your files if you haven't protected yourself against them.

Virus protection

In anticipation of a millennial surge in viruses, Microsoft recommends the installation and use of current virus-protection software, and the company has teamed up to make free 90-day trials of several anti-virus solutions available.

For more information, see www.microsoft.com/y2k/antivirus/AntiVirus.htm.

One particularly well-regarded anti-virus application is Symantec's Norton AntiVirus 2000, which can automatically scan your disks, downloads and e-mail messages for viral invaders.

AntiVirus 2000, which costs around $40, includes a 12-month subscription for updates to deal with the latest viruses. You can schedule the application to download these updates automatically as often as once a week (think of it as the equivalent of a booster shot).

This way, you can create a safe zone on your computer: a folder into which any file you drop will automatically and immediately be scanned for viruses. The application can also help identify and report new viruses.

Versions for both Windows and the Macintosh are available.

Christopher Ott is a freelance technology writer and author of "Global Solutions for Multilingual Applications" (Wiley, 1999).