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What is a Computer Virus?

We've all heard about various types of computer viruses and have had warnings to watch out for them. But what exactly is a virus?

There are actually four types of programs that can invade computers and damage them:

1. Virus: A virus is a program that automatically copies itself - either from one disk to another, from a disk to a hard drive (or vice versa), or from one computer to another via a network, or internet connection. Usually the user is not aware that this is happening. The virus then can either play some kind of trick or disrupt the operation of the computer. Some viruses are designed to change or destroy computer data.
    
2. Trojan Horse: A Trojan Horse is software that pretends to be a useful program such as a game, document, screensaver, etc. Hidden in the software can be a virus, a trapdoor that allows intruders to enter your computer, or a bomb that causes damage when triggered. In most cases, Trojans cause damage from the moment they are run. So the only thing that you may be able to do about them is erase a few files or programs, and hopefully you will have backups so that you can replace them.
    
3. Worms: A worm is a program that does not need to piggy-back on top of other programs to do their damage. They are sophisticated programs that can travel the Internet, use different password combinations to get into computers or files, and look for loopholes in programs that are running on they computers they target.
    
4. Bombs: There are two different types of bombs: logic and time bombs. A time bomb is set to do it's damage when a certain date or time is reached. A logic bomb monitors the activity on a computer until a certain predetermined event takes place (for example if you use a certain combination of keystrokes, or enter commands into your computer in a certain order). The end result could be merely an annoying message flashing across your screen - or it could wipe your entire hard drive.
    

How Can I Tell If My Computer Has a Virus?

• Is your computer taking longer to start up all of a sudden?
• Did you suddenly run out of disk space on your computer, even though you haven't added anything recently?
• Does the drive light keep flashing - even when you are not doing anything?
• Are there new files appearing on your hard drive - ones that you didn't create, and didn't come with a known software installation?
• Are your file names changing? Do they suddenly have different extensions?
• Do program sizes keep changing?
• Is your computer sending out emails that you didn't write?
• Are your computer's CMOS settings changing?
• Do you need to boot up from a CD or floppy in order to be able to access your hard drive?
• Do you keep getting 32-bit error messages?
• Is your CD-ROM drive opening without anyone using the computer?

How can I Protect my computer against viruses?

There are several things you can do to protect your computer against viruses:

1. First, make sure that any software you install on your computer comes from a reliable source.
    
2. Be careful about opening email attachments - especially if you are not expecting anyone to be sending you something as an attachment. If you don't know what it is, or why it's being sent to you, then it's best to delete the email without opening the attachment immediately.
    
3. Back up your work regularly. Make copies of any important files you need to keep and store them on disks, or CDs so that if you end up having to reinstall your operating system, all you have to do is copy over your files instead of starting from scratch. Make sure your disks are write-protected after you've got your info on them.
    
4. Run antivirus software on a regular basis to make sure any virus programs are caught.
    
5. Check for software patches for applications such as Internet Explorer, Outlook, and other browsers and email programs. Download the appropriate patches. This will help keep worms from exploiting any security flaws in your system.

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Page last updated January 26, 2008