What Are Viruses, Worms and Trojans?

Viruses, worms and trojans are malicious programs that can cause damage to your computer and the information inside it. They slow down the Internet and can even spread themselves to your friends, family, co-workers and the rest of the Web. The good news is that with just a minimum amount of prevention and some common sense, you can be less likely to fall victim to these invaders.

On this page

• What is a virus?
• What is a worm?
• What is a Trojan?
• How do viruses spread?
• How can I tell if I have a virus?
• Reducing your virus risk
• Anti-virus Software Vendors

What is a virus?

A virus is a piece of computer code that attaches itself to a program or file so it can spread from computer to computer, infecting every computer as it travels. They can damage your software, your hardware and your files.

What is a worm?

Like a virus, a worm is designed to copy itself from one computer to another, without user action. It does that by taking control of features on the computer that can transport files or information. Unfortunately, a worm can travel alone and replicate itself in great volume. It has the tendency to send copies of itself to everyone listed in your e-mail address book, and their computers would then do the same, creating a domino effect.

What is a Trojan?

A Trojan is a computer program that appears to be useful but actually does damage. They spread when unsuspecting people are lured into opening a program because they think it comes from a legitimate source. You can also get them in software you download for free. Because of that, never download software from a source that you don't trust.

How do viruses spread?

Virtually all viruses and many worms spread by opening and running infected programs - like e-mail and the files that are sent along with e-mails.

• Never open anything that is attached to an e-mail message unless you were expecting the attachment and you know the exact contents of that file.

Other viruses spread through programs you download from the Internet or from virus-ridden computer disks that you borrow from friends or even buy in a store.

How can I tell if I have a virus?

You might not know you've contracted a virus, even when you open and run an infected program. Here are a few of the more common symptoms:

• Your computer may slow down.
• It may stop responding.
• It may crash and restart every few minutes.
• When you power up, you can be stuck staring at a blank screen.

Reducing your virus risk

Nothing will guarantee the security of your computer 100 percent. However, you can continue to improve your computer's security by keeping your software up to date and maintaining current anti-virus software.

You can protect your computer in three steps:

• Use an Internet firewall
• Get computer updates
• Use up-to-date anti-virus software

Anti-virus software vendors

Anti-virus software is software that is specifically designed to detect and prevent viruses. It is highly recommend that you use anti-virus software on your computer. Following is a list of independent anti-virus software vendors.

The installation process will vary for each anti-virus vendor, but it is critical to remember these three issues for every anti-virus package:

• Download or install the program from CD.
• Read through the agreement to understand the terms of service - if there is a special trial of the product, understand how to continue service after the initial offer expires.
• Make sure to keep the program up-to-date following the vendors instructions, please note that updates to your anti-virus software will not occur through Windows Update.