As you might suspect, a computer "virus" means trouble. But exactly what kind of trouble? Does your PC break out with fever and chills?

Not exactly. Here, however, are some symptoms your computer might display:

• Inability to start (boot up)
• Longer than normal startup times
• Unpredictable program behaviour
• Unexplainable file size changes
• Strange graphics appearing on the screen
• Strange sounds coming from your computer

Clearly, a computer virus is something to avoid.

	TIP: Many worms and viruses spread to a PC when web page scripts are run in your browser. These scripts typically provide interactivity on the page. You can turn off browser scripting in Internet Explorer (IE) by selecting Tools, Internet Options, Security and clicking Custom Level. Disable Download unsigned ActiveX controls, Initialize and script ActiveX controls not marked as safe, Active scripting, and Scripting of Java applets.

Virus Basics
A virus is a computer program intentionally written and released to spread across computers and networks and disrupt your computing experience. These bad-mannered programs come to your PC through e-mail, the internet, downloaded files and files you open on a CD. Viruses typically work by attaching themselves to another program on your PC, and do not infect the computer until the program runs.

Other bad-behaving programs are often grouped together with viruses, but are technically different. These include:
Worms — A worm is similar to a program but doesn't need to attach itself to another program to run.
Trojans — A Trojan poses as a legitimate program but is designed to disrupt computing on the PC it infects. It is not designed to spread to other computers.
Backdoor Trojans — This type of code allows other computer users to gain access to your computer across the internet.

Here are examples of viruses, worms and Trojans released over the past couple years and a description of the havoc they raised:
DLoader-L — This Trojan arrived in a seemingly legitimate e-mail, and then it downloaded and installed another program on a PC. This program then allowed computers to be controlled by a third-party to attack websites whenever they connected to the internet, all without the PC owner's knowledge.
Bugbear-D — The worm recorded keystrokes, including passwords, and gave the virus writer access to them. The Compatable virus made changes to data in Excel spreadsheets. And the Sircam worm deleted and overwrote data on hard disks on a specified date.
Chernobyl (CIH) — This virus overwrote system BIOS chips on PCs, rendering them unusable. The Netsky-D worm made computers beep sporadically for several hours. And the Cone-F worm displayed a political message and mailed itself to other computers.
MyDoom — This worm e-mailed itself to addresses found on the infected computers. This generated so much e-mail traffic that e-mail servers slowed to a crawl or crashed. Companies responded by shutting down servers and mail service.

A virus will not only cause you grief, but also your customers and business partners if you forward one to them. You'll be embarrassed, have your reputation damaged and the infected party may want you to compensate them for any damage done.

Staying Out of Trouble
The worldwide market for antivirus software now takes in over (US) $1 billion in revenues annually. Installing commercial grade antivirus software should be as standard as the space bar on your PC. Most new PCs come with trial versions of antivirus software pre-installed to provide protection from the moment you turn the machine on.

Because new viruses are released all the time, make sure you set up your software to automatically download updates to keep your protection current. Also make sure to renew your subscription to the update service annually.

Other Action to Take
Remember to implement these safe computing practices to enhance the protection provided by antivirus software:

• Establish an e-mail policy. Implementing e-mail and internet use policies can help ward off virus infections. For instance, you and your employees should know to delete any e-mail that looks suspicious, and to avoid downloading any unauthorised programs, documents or even screensavers.
• Use firewalls. If you have broadband internet service, turn on the software firewall included with Windows XP Professional. Also consider installing an inexpensive device called a broadband gateway at your internet connection. The gateway will bounce back worm attacks that otherwise would reach your computer.
• Run Microsoft Update. Microsoft Update is a built-in tool that helps keeps the Windows XP operating system protected against viruses. It alerts you when add-ons to Windows are available to prevent a virus attacks. You can then download the add-on for free and have Microsoft Update automatically install it. You can also have the entire process carried out with no effort required from you.

If fighting computer viruses sounds like an uphill battle, it is. But there is some good news. In 2004 more virus writers and hackers were captured, arrested and sentenced than in any previous year.