Last week's Power Computing column had a suggestion for avoiding the Michelangelo virus that might not work in some cases. The virus, which has been spotted in computer systems nationally, damages personal computer data when the computer is turned on March 6, the anniversary of the artist's birth. The column said users could avoid the virus by turning on their computers March 5 and leaving them on until March 7. This will work in most cases, but if there is a power failure, many personal computers will automatically reboot themselves. Thus, a power failure on March 6 would have the same effect as turning on the computer on March 6. (Published 3/2/92)

Were he alive today, Michelangelo would be 516 years old on March 6. But before you plan a birthday celebration, be aware that it's also the day that a pernicious computer virus could destroy the data on your PC's hard disk.

The Michelangelo virus, which will irrevocably erase all the data and software from any infected system, is the latest in a surge of viruses to target computer systems.

Fortunately, there are some easy-to-use and inexpensive programs that will detect and remove it and other viruses.

There are several ways that viruses can infect your computer -- they can invade from other people's floppy disks or from programs that are downloaded from a dial-up computer bulletin board. Viruses can also be transmitted over local area networks that companies use to connect their PCs. A survey by Dataquest and the National Computer Security Association revealed that 63 percent of corporate PC sites have encountered a virus.

Most viruses attach themselves to programs and are activated when the infected program is run. What happens next depends on the virus. Some just display a message. Others slow down your system or multiply themselves, taking up valuable disk space. Some delete one or more files. The worst ones destroy all the data on your disks.

Michelangelo is known as a "boot sector infector." It's not carried by programs but is spread by floppy disks. It attaches itself to the area of the disk that is read when the computer is "booted," or started. You can catch the virus if you boot or turn on the computer while an infected floppy is in the A drive. You can't get the Michelangelo virus from programs that you download from computer bulletin boards or on-line services.

Although most software companies scan their disks for potential viruses, it's possible, though unlikely, to get a virus from a commercial program. Computer maker Leading Edge reported that it had inadvertently sent out 500 machines with Michelangelo on the hard disk.

The virus could already be lurking in your PC's memory. When you start an infected computer, Michelangelo copies itself into memory where, on any day other than March 6, it sits quietly occupying about 2 kilobytes of RAM. On March 6, the virus overwrites the infected hard disk with garbage data.

Chances are you're not infected, but you never know. I found the virus on my machine. Considering the consequences, I recommend that you take precautions. You could avoid the issue by simply not turning on your computer on March 6. Or you could start it on March 5 and leave it running until March 7.

But there is a much better solution.

The best way to protect yourself from this and other viruses is to use one of the virus detection and elimination programs that scan your disks and memory to determine whether you have a virus. If so, the program will remove it from memory and from the disk. These programs can also help prevent an infection by scanning programs and disks.

Any of the reputable anti-virus programs will detect and remove Michelangelo and other known viruses. It's important that you have a recent version. The Michelangelo virus wasn't discovered until April 1991, so older versions of anti-virus programs won't do you any good.

The leading anti-virus programs include Norton Anti-Virus ($129 from Symantec, 1-800-441-7234), Untouchable ($145 from Fifth Generation Systems, 1-800-873-4384), Dr. Solomon's Anti-Virus Tool kit ($149.95 from Ontrack, 1-800-752-1333) and Central Point Anti-Virus ($129.95 from Central Point Software, 1-800-445-4208). All prices are suggested retail.

McAfee Associates (telephone: 408-988-3832) publishes shareware and commercial anti-virus software. Modem users can download the shareware version from CompuServe and many computer bulletin board systems for no cost other than connect time or phone charges. Users are expected to pay a registration fee to the company.

In response to the specific Michelangelo threat, Symantec is offering a free version of Norton Anti-Virus that detects and removes the Michelangelo virus only. It is not effective against any other virus. Modem users can download a copy from CompuServe or Symantec's bulletin board (telephone: 408-973-9598) or you can order a disk for $9 shipping and handling by calling 1-800-343-4714, extension 707. Some computer dealers will provide this disk for little or no charge.

If all is well March 7, you can breathe a sigh of relief. But don't get relaxed. The Jerusalem virus, which deletes infected programs when they are run, is scheduled to do its dirty deeds a week later on Friday the 13th.Write to Lawrence J. Magid, P.O. Box 620477, Woodside, Calif. 94062, or contact the L. Magid account on the MCI electronic mail system.