Catching a computer virus can be a nightmare for a netrepreneur. A virus is a malicious program or a piece of malicious code incorporated into another file. Once it's on your system, a virus wreaks havoc by corrupting, erasing, attaching to, or overwriting other files. The general term "virus" applies to several different kinds of disruptive programs that range from the annoying to the downright destructive.

Many viruses cause mischief but no serious damage (playing an animation, displaying a never ending series of popup windows, etc.). The more malicious types might erase your data or make it inaccessible, commandeer your hardware, corrupt critical system files, or even disable your computer or network completely. The worst can destroy critical system files or even cause damage to your computer hardware.

Often the virus remains undetected and lies dormant until a certain date arrives or some action on your part activates it. It might replicate itself by infecting other files on your computer, attach itself to your outgoing emails, or infecting any files you create with certain programs. The virus could attach itself to your outgoing emails or even email itself to everyone in your address book without your knowledge.

At the very least, catching a virus will result in wasted time and considerable stress and frustration. At worst, it might destroy irreplacable information and put you out of business until you can remove the virus from your system and undo any damage it has caused. There are actually several different types of malicious programs you need to be aware of, including:

Macro viruses:  Macro viruses can exist inside any document associated with an application that uses a macro language (for instance, Microsoft Word). If you import an infected file into your computer (via floppy disk or email attachment) your system becomes infected. Typically the virus makes itself part of a default "template" and thus infects each new file you create.

Trojan horses:  A Trojan horse is a malicious program that pretends to be a benign application. It may destroy files or enable intruders to access just about any file or data. It's different from a virus or worm in that it does not replicate itself, but it does wreak havoc with your computer and can be just as destructive.

Worms:  A "worm" uses your computer to infect other others' systems via networks (including the Internet). It stays in your computer's memory (usually undetected) and uses automatic features of your operating system to send copies of itself to other computers, for instance, via email or Internet Relay Chat (IRC). In other words, your system is used as an unwitting host while the worm does its dirty work. The most malicious worms can even disable your anti-virus software!

Back door programs:  These are small software programs that install themselves on your system without your knowledge, and create a "back door" within your computer that gives outsiders access to your system. The perpetrators might be interested in monitoring your Web surfing habits or the objective could be stolen passwords or even identity theft.

Viruses are designed to spread quickly and escape detection, and people often pass the virus along without even knowing they have it. Protecting yourself from viruses is tricky because new viruses (amd even completely new types of viruses) are being developed all the time. Viruses are bound to remain a fact of life online, so a virus is bound to come your way sooner or later. Fortunately, some simple safety measures and vigilance will go a long way toward keeping your system virus-free.

It used to be the case that you could only catch a virus through launching an executable program file (one with the extension ".exe"), but that is no longer true. Reading email, launching an executable file, or just visiting a website could all put you at risk. Viruses can now be written into almost any type of file. Hackers and the creators of viruses are notoriously inventive and are constantly devising new viruses and ways to spread them. The most common ways to catch a omputer virus are:

• Reading email.  Unfortunately, just opening an email message may be enough to infect your system. In fact, opening email is the most common way to catch a virus. Don't count on being able to recognize a potentially infectious email by the subject line (which is often fictitious) or the file type of the attachment. Also, remember that it's quite possible to catch a virus from a "trusted source", because the sender may not know their system is infected and could be spreading the virus unintentionally.
  
  
• Opening email attachments.  Email attachments of any kind can potentially carry a virus. Even if an email itself is safe, an attached file might not be. Be especially cautious about cryptic emails from unknown sources that include an attachment. Unless you were expecting the attachment and know the sender, don't take a chance.
  
  
• Downloading and installing software programs.  Net surfing is an increasingly common way for computers to become infected. You might unknowingly download an infected file from a website or be infected with an insidious program just by visiting a website. Don't download any kind of program unless you're confident the website you're visiting is reputable, particularly freeware or shareware.
  
  
• File sharing  Viruses can be spread through exchanging files via floppy disks, Zip drive storage disks, CD's, and over networks. If you loan a diskette to someone whose computer is infected with a virus, it may infect your computer when it's returned. If you use two computers in different locations, or a laptop plus a desktop, you could infect one computer with files from the other. Or, if you own two computers and you share or transfer data between them, both computers will become infected by viruses on either. Sharing files via the Internet and email carries the same risks.

You should try to stay informed about new and emerging viruses, but don't rely on that alone to keep you virus-free. By the time you find about a new virus threat, it may be too late. The best protection is caution on your part plus up-to-date anti-virus software. Here are the steps you can take to protect your system:

• Buy a good anti-virus utility and use it.  Your local office supply or computer store should have several to choose from, plus you can find many downloadable programs on the Web. The purchase price includes frequent updates of the virus definitions so you will be protected against new viruses as they emerge (usually you can schedule automatic updates via the manufacturer's website). Scan all the files on your hard drive when you first install the software, then set it to scan all incoming files before you open them.
  
  
• Scan everything.  Once you've installed your anti-virus program and made sure it's up-to-date, let it scan your entire system. Then have it automatically do a complete system scan on a weekly basis. Also set it up to always scan any files before opening them, including email attachments of all kinds. The best time to detect an infected file is before you open it (once it's opened, the damage may already be done). Make sure your anti-virus software is always running when you're using your PC.
  
  
• Back up your important data.  After scanning your system to make sure it is virus-free, do a complete backup of your important files and then schedule periodic backups going forward. Keep your original software application CD's in a safe place, along with your emergency boot disk (if you didn't receive one when you purchased your PC, create one by following the manufacturer's instructions). If you do get a virus, you might need these in order to restart your system.
  
  
• Protect all your computers.  If you use more than one computer, protect them in the same way by installing anti-virus software, scheduling periodic scans, and backing up data on each. If you have employees who use the computers insist they take the same precautions. Remember that one computer can easily infect the others, so leave any system vulnerable.
  
  
• Screen your emails.  If you receive an email from an unknown source, the safest bet is to delete it. But even if it does appear to come from someone you know, a virus could be hitchhiking along without their knowing it. Also, a virus could have commandeered their computer and emailed everyone in their address book without their knowledge. Virus-bearing emails often contain an enticing subject line or attachment so you'll be tempted to open them, but remember, just opening an email can be enough to infect your system.
  
  
• Be very cautious about opening attachments.  Be particular careful when opening any email containing attachments, particularly if you don't recognize the sender. Tell friends and colleagues to notify you before sending any email attachments. When you receive an email with an attachment from someone you know, save the attachment to a floppy disk, scan it using your anti-virus software, and only save it to your hard drive when you're sure it's not carrying a virus. Even if the body of the email itself is safe, the attachment might not be.
  
  
• Think before you click.  A clickable hyperlink within the body of an email message could lead you to a Web page that infects your computer with a malicious program. Unless you know and trust the source, you're taking a chance by following those links.
  
  
• Be selective about reading HTML-formatted email.  HTML ezines, electronic newsletters and email messages could potentially contain scripts that harbor a virus or other malicious program. Be selective about opening emails formatted in HTML, and don't subscribe to the HTML version of an ezine or newsletter unless you know and trust the publisher.
  
  
• Delete suspect emails without previewing.  If your email client software lets you automatically preview each email message, your system could become infected just by viewing a message in the preview pane or right-clicking on a message to delete it. Turn off the preview feature to be on the safe side.
  
  
• Download discriminately.  Be conservative about downloading or installing programs, applications, and utilities you find on the Web, particularly if they are "freeware". Plenty of nice people develop useful programs and give them away for free in the spirit of sharing, but there are others who have ulterior motives.
  
  
• Don't run programs of unknown origin.  Never run a program unless you know for sure it was authored by a trustworthy person or company. Also, don't send programs of unknown origin to friends or coworkers, no matter how amusing or entertaining, because they could contain a Trojan horse program.
  
  
• Plug any security holes.  Download any security patches for your operating system and applications as soon as they become available. If you register your hardware and software soon after purchase, the manufacturer will probably notify you by email you about any security "holes" and the appropriate fix (usually, a free download from the manufacturer's site).
  
  
• Stay informed.  Keep your eyes open for new viruses that surface, the methods by which they spread, and the symptoms of infection. Sometimes certain software applications are vulnerable to a new virus but you can visit the manufacturer's website and obtain a free "patch" to avoid being infected. If you don't already have the latest updates, visit your anti-virus software website and download it. Keeping abreast of new viruses can give you added safety.
  
  
• Be skeptical about virus warnings.  Many times the emails that masquerade as virus warnings are actually carrying a virus! They may urge you to pass on the warning to all your friends; if you do, you're simply spreading the virus. Go to one of the reputable anti-virus websites to get information about emerging viruses and fixes, and don't forward any email warnings you receive to friends and colleagues.

In spite of all these precautions you could still find yourself dealing with a virus that is trying to invade your system. If your anti-virus software scans a file and detects a virus, you will probably given the choice of cleaning the file if that's possible or deleting it if it's not.

• Just hit "delete".  Getting rid of the infected file altogether is the safest action. If the infected file is an email or email attachment, simply delete it immediately without opening it. If it's a file or program on a diskette or the Web, don't download, open, or launch it. If a file that's already on your computer's hard drive is infected, just delete it unless it's a file you just can't do without (but in the future, you should keep virus-free backup copies of any critical files).
  
  
• Clean it if possible.  If you have an infected file that you need to salvage, you can try "cleaning" it if you're given the option. That means the file can probably be repaired by the anti-virus software and made safe to open. If the file can't be successfully cleaned, your software will let you know. In that case you'll need to delete the file and scan all the other files on your computer, since they may be carrying the virus as well.
  
  
• Do some research.  Find out what you can about the specific virus that's infected your system. Visit anti-virus resource sites to see if it's listed or enter the name of the virus at a search engine site. You'll probably be able to find out the method and consequences of infection, how to rid yourself of the virus, and how to keep from catching it again.
  
  
• Alert others who might be infected.  If you suspect you've accidentally infected friends, colleagues, or coworkers, alert them right away and provide whatever helpful information you can and advise them to delete any unopened emails they've received from you.
  
  
• Trace it to its source.  Figuring out how you caught a virus can be tricky, especially since you don't always know right away that your system has been infected. If you are pretty sure the virus came with an email from someone you know, tactfully inform them that their computer seems to be infected with a virus and they are inadvertently spreading it to their friends and colleagues.
  
  
• Report it.  If you believe you caught a brand new virus, report it to one of the major anti-virus sites. Give them whatever information you have about how you were infected and what damage, if any, the virus caused. That way they can update their virus definitions to protect others from infection (and perhaps provide a "fix").
  
  
  

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  Related resources:
  
  McAfee virus information
  Symantec virus information
  F-Secure virus and hoax information
  
  
  Related articles:
  
  Cutting Down on Spam
  Managing Your Email