Unless this is your very first time on the Internet, you have no doubt heard of computer viruses and the damage they can cause. Every day it seems there are reports of a new 'strain' being unleashed upon us unsuspecting Netizens to wreak havoc on our systems.  So, what is a computer virus, how exactly can it affect you, and what should you do to protect yourself from these malicious programs?

Computer viruses are bits of code that damage or erase information, files, or software programs in your computer.  And just as in humans they can spread.  A computer can 'catch' a virus when you download an infected file from the Internet or copy a contaminated file from a diskette.  Once a computer is infected, the virus may immediately start to damage or destroy information, or it might wait for a particular date or event to trigger its activity.

Common symptoms of virus infection may include strange characters and/or messages suddenly appearing on your screen, hard drive errors, memory errors, software errors, and corruption of files and directories.

Computer viruses do not infect the following; files on write-protected disks, documents (except in the case of Word macro viruses, which can only infect documents and templates written in Word 6.0 or higher), compressed (.zip) files (however, applications within a .zip file could have been infected before they were compressed), or computer hardware, such as monitors or computer chips.  They only infect software, most often executable (.exe) files.  In addition, Macintosh viruses cannot infect DOS-based computer software and vice versa.  For example, the infamous Michelangelo virus does not infect Macintosh applications.  Again, an exception to this rule are the Word and Excel macro viruses, which infect spreadsheets, documents and templates that can be opened by both Windows and Macintosh computers.  Finally, some viruses may not necessarily let you know that they are there - even after they do something destructive.

Viruses spread when you launch an infected application or boot your computer from a hard disk or floppy diskette that has infected system files.  If a program contains a virus, the virus activates when you execute, or run, the program.  Once a virus is in memory, it usually infects any application you run, including network applications if you have write access to network folders or disks.  Different viruses behave in different ways. Some stay active in memory until you shut off your computer.  Others stay active only as long as the infected application is running.  Turning off your computer or exiting the application removes the virus from memory, but does not remove the contaminated file.  That is, if the virus resides in a system file, the virus will activate the next time you start your computer.  If the virus resides in an application, the virus will activate again the next time you run that application.

The best defense against computer viruses is to avoid potential sources, such as file downloads, shared diskettes, and those innocent-looking email attachments.  Never download anything from anyone you do not know and be wary of all downloadable files, including those from friends.  Often infectious files are passed on without the virus having been detected.  If you do choose to download, purchase a good anti-virus software program and use it often.  Run those email attachments and borrowed diskettes through the software before executing them.  One unsuspecting victim's computer contracted a boot-sector virus by allowing his system to boot on an infected floppy loaned to him by a friend who mistakenly claimed that it was virus-free.  The antiviral software he had used to check it was older than the virus itself.  For this reason, it is extremely important to always be sure your anti-virus software current.  The leading virus-detection software manufacturers include Data Fellows, Symantec (Norton), Dr. Solomon's Software, and McAfee.  Most offer free evaluations so you can try before you buy, and some feature free upgrades/updates after you buy.  Look for a product that utilizes "on-access scanning" which runs constantly in the background.

If you think you may already have a virus, anti-virus software is the best cure.

Related Resources:
Certified Anti-Virus Products (outside link)
Word Macro Protection (outside link)
What To Do If You Have a Virus (outside link)

In next month's edition: Virus-warning hoaxes and how to identify them.

This article written and prepared for the Eureka Today Newsletter by J. Brown aka: jem3030, a CL with experience in tracking hoax and virus information we receive in GeoCities. Before you act on e-mail that might be misinformation you should follow through on the above posted material to confirm whether you have received a bona fide message, or determine if it was a time-consuming hoax.