What Is a Virus?

Start talking computer virus to someone and there eyes go blank. Why? It's a conversation not unlike that regarding root canal. No one really likes to talk about them: they're uninteresting and basically they're about as fun to talk about as hemorrhoids.

Viruses though are part of our digital world, and much like smallpox and other human diseases, they are here to stay. We just can't get rid of them. But what are they exactly? Why can't we eradicate them once and for all?

Well, there are several forms viruses take (okay, let the eyes start glazing over). We can foresake the discussion of some of the older more anachronistic types (at least initially) as they don't make the rounds as frequently anymore. So, how do email viruses work?

Simplistically, you get an email with an attachment. You are led to believe the attachment is a picture, video clip, audio clip or whatever. You double-click on it and Windows looks at the extension of the attachment and runs the appropriate program.

So if someone sends you a picture file that ends in .JPG or .BMP or dozens of other extensions, Windows will run whatever program you have set up to view pictures with. If someone sends you an attachment that ends in .DOC or .DOT, Windows will run Word. XLS, .XLW, .XLT will cause Windows to run Excel, etc.

If someone sends you an attachment that ends in .EXE, .BAT, .COM, .SCR or dozens of other endings (extensions), Windows figures you want to run the program or system command. Click here to see a list of executable file extensions.

So someone writes a program that basically says:

Open Outlook

For each contact in the Address Book do the following

    Email.ToAddress = the contact's email address

    Email.Subject = "Click me!"

    Email.FromAddress = your email address

    Email.Attachment = my virus program

    SendEmail

Next Address

Close Outlook

Save my virus program as c:\windows\virusprogram

Hide the program

You get the program, double-click and the next thing you know you're getting nasty emails from friends claiming you sent them a virus and now they're infected. Ooops! How would you know?

Well, for one, you should be smarter than that! You should never double-click on anything remotely suspicious.

Next: Other Nasty Things Viruses Do