What is a virus?

A computer virus is loosely defined as program or code that makes copies of itself when it's opened and does nasty things to your computer. Some antivirus software vendors say that a computer virus is any program that replicates itself. Others say that a virus can be any ill-intentioned program. Virtually every virus tries to do one thing first: spread to other programs and data files on your hard disk. When you boot up from an infected disk, open an infected file or run an infected program, the virus's code is copied into your computer's memory. From there, the code usually attempts to attach itself to other files. The virus may also alter data-file contents, cause program crashes, display annoying screen messages, degrade system performance or even destroy all of your disk files. There are even viruses that can detect your e-mail program, and then compose and send messages with infected attachments. The only bright spot: your hardware is pretty much safe, although some can destroy your monitor by changing the settings in ways your monitor can't handle.

Virus "experts" classify viruses into many categories, such as virus, virus carrier, Trojans, and more. The bottom line is, you won't be able to tell which is which if you're infected. A virus can be anywhere: a file you've downloaded, an e-mail attachment, or even a web page.

Virus types

According to statistics compiled by the National Computer Security Association, most of the viruses currently reported are Microsoft Word macro viruses , with the number of known macro viruses growing from about 50 to more than 1,000 in the past year. A macro virus lodges itself within the document or macro templates used by certain applications, primarily Microsoft Word, although Excel, Lotus, and others can also catch a macro virus. A macro virus is spread mostly through e-mail as an attachment with a .doc ending. Just opening one document with a macro virus can infect all your documents, plus all new documents you create on that computer.

Boot Sector Viruses.
These infect a diskette's or hard disk's boot sector, which is normally read by the operating system at bootup or when the disk is accessed. Typically, a boot sector virus spreads when an infected diskette is left in the A: drive and the PC is rebooted. Boot sector viruses may interfere with the startup process or destroy the disk's directory table.

File Viruses.
A file virus's code attaches itself to executable files (*.exe and *.com) From there, the code may infect other applications.

Multipartite Viruses.
Multipartites are distributed in one format and then transform to another. They may, for example, begin by inf ecting the master boot record and then move on to attack EXE or COM files.

Stealth Viruses.
A stealth virus disguises its presence in memory or on disk. A stealth virus that has corrupted a drive's boot sector may intercept a request from diagnostic utilities examining the boot sector and transmit a false image of the original, uninfected boot record.

Polymorphic Viruses.
These viruses dynamically change their code as they spread from file to file, making detection difficult.

As of this writing, WM.Concept, a Word macro virus, is believed to be the most prevalent, followed by Form.A, a boot sector virus, and One Half.3544, a multipartite boot sector virus that also infects COM and EXE files.

How can I tell if my system is infected?

A virus is capable of anything its author wanted. Some are on time delay, so they "sleep" until a specific day of the week, someone's birthday, or even phases of the moon. So you may have a virus even now! Some things you can watch out for are unexplained disk activity, files that have been changed(included Last Modified date changes), menus that won't open or commands that don't work, even slower-than-normal performance of your computer. However, these symptoms can be caused by legitimate programs. Find Fast, installed with Microsoft Office, searches your disk for Office documents every hour, causing noticeably slower responses.

Unusual system performance may indicate a virus is at work. Your system may run more slowly than usual; programs may crash unexpectedly or start exhibiting strange behavior (menus won't open, files can't be saved and so forth). In the worst cases, directory listings may be garbled or the system may refuse to start. Other symptoms to watch for include changes in the file size or time and date signatures of common system programs. If you notice any of those symptoms, stop using the PC and install and run an antivirus program as soon as possible.

What can I do to prevent an infection?

Disable program features that automatically open e-mail attachments or launch downloaded program files. Look for a menu item called Preferences, sometimes under the File menu.

Create an emergency boot disk for your computer and write-protect it by flipping the little plastic switch on the back.

Don't open Word documents (.doc) with Word unless you know it isn't infected. All Windows computers have a program called WordPad (Start --> Programs --> Accessories) that isn't capable of being infected with Macro viruses.
Here's how to open .doc files with WordPad:
Hold the Shift key down, and right-click a .doc file. On the menu that pops up, select Open With... Scroll down to WordPad, make sure the check box that says "Always use this program to open this type of file" is checked, and click OK. Now any time you open a Word.doc file, it will open with WordPad. (To open it with Word, right-click the file and select Open.)
Here's a much more complicated, but much cooler way:
Double-click My Computer on your desktop, then click View --> Folder Options -->File Types. You'll see a list of all the registered file types on your computer. Scroll down to Microsoft Word Document (it should be there, unless you've installed another program that changed it.) Click the Edit button. Close to the bottom is a field called Actions: with a line of buttons below it. Click New, then in the box that pops up, type in WordPad in the top field, then click the Browse button, navigate to WordPad on your disk, and click it, then click OK. You've made a new file association! Highlight it and click the Default button.

The most important tip: Get an Anti-Virus program if you spend any time on the web at all! They cost about $40 to $60, which is less than you'll spend per hour with a computer guy, trying to get rid of a virus. Look for an anti-virus program with on-demand web updates. New viruses are created every day; if you aren't updating your anti-virus software, you aren't protected. Keep your anti-virus program up-to-date!!

Don't have money to spend? Go to any download site and search for 'anti-virus'. There are many free anti-virus programs, but remember: you get what you pay for.