Are the cookies that reside in your computer necessary? Sometimes yes.

Let's say you use the Internet Explorer browser to access the Web. Each time you download a page, your computer accesses a Web-server computer where the page resides. The server, which could be housed anywhere in the world, downloads the page to your computer and Internet Explorer displays it to you in a viewable format.

The Web server, now that it has given you what you requested, goes off to do something else. It closes the connection to your computer and then forgets who you are. If you now click on a link on the page you downloaded that also resides on the same Web server, the server will dutifully download it to your computer. However, it does not remember who you are. From its point of view, every single request to do something it receives is a unique request from a different computer.

This system worked well for the Web's original use: to be a vast electronic library. It was designed to support the simple reading of text. Since those early days, images, videos, sounds and commerce have been improvised to work on this underlying fundamental structure.

Now let's take another example. Say I want to buy a book, using a credit card, from Barnes & Noble online. I enter my name and address on a Web page. Then I am sent to a new Web page to enter my credit-card number. Since the Web server does not know I am the same person, how can it relate my personal information to the credit-card information? Answer: It gave my computer a cookie.

How does it work? First, when I begin browsing the Barnes & Noble site, it sends a small text file to my computer. This file can only be referenced by the Barnes & Noble Web server. It contains a simple but unique number that identifies me. When I go to buy the book, the Web server tries to read this cookie to identify me. It does the same thing on the credit-card page. Thus it knows I am truly me throughout the buying process and can relate the personal information to the credit-card number.

The next time I return to Barnes & Noble to buy something, up pops all my information – since the computer now knows who I am. The unique cookie, which resides on my computer and my computer only, becomes a means of identification. For those Web sites where you actually enter a username and password, these would then be contained in the cookie, the password being encrypted. Cookies can also contain preferences you have chosen on customizable Web sites.

Cookies give a Web developer helpful clues about who's visiting his site. This can help him determine what appeals to his audience. With the proper cookie scheme, he can tell which demographic group goes where on his site and how many people are interested in a particular product or service. He can even use cookies to tell whether a particular column or advertisement is attracting enough attention to keep it around. For the maintainer of a Web site, this information can be invaluable.

Maybe you're among the people who don't like the idea of one's computer silently being “force-fed” files from an outside server. Is there reason to be afraid of the cookie monster? It depends on what sort of things scare you.

Cookies can be set to expire (they'd be automatically deleted) when you exit a Web page or remain on your computer far into the future. Various advertising companies abuse this feature. Cookies on your computer can be created and read whenever a Web server downloads any object to it. This includes banner advertising or any graphic advertisers may place on a page.

Every time you visit a page with an advertising graphic from the same agency the graphic effectively asks, “Have I seen this person before?” If the answer is “Yes” (a cookie exists on your computer from them), then a notation is made in your profile on the advertiser's computer system. In a short time, the advertising agency can acquire quite a bit of knowledge about your surfing habits.

Why do advertising agencies do this? Because by knowing what you like to look at they can tailor their advertising to appeal to you. I can all but guarantee that the largest advertising agency on the Internet, Doubleclick; has a cookie on your computer. To find out, launch Internet Explorer and go to Tools > Internet Options > Settings > View Files. (AOL users can select on their screen Settings > Preferences > Internet Properties > Settings > View Files.) You should see a cookie called doubleclick.net. You can find out when it expires, was last modified and was last accessed.

So how concerned should you be about cookies? Well, that depends on how bothered you are by advertising agencies tracking your surfing habits. With the above technique you can look at the cookies on your computer and delete those you don't recognize. Want to get rid of all of them? On Internet Explorer go to Tools>Internet Options>Delete Cookies. (On AOL, it's Settings>Preferences>Internet Properties>Delete Cookies.) The downside of deleting all cookies: They make using your favorite sites quicker and easier. Then again, you can always set them up again next time you shop at or interact with the site.

There's lots more to cookie-management. It's one of the features with which you ought to acquaint yourself if you spend a considerable amount of time on the Internet.

I don't know whether computer cookies got their name from real cookies, Chinese fortune cookies or what have you. Perhaps one of my readers knows the origin of this name. I do know that, personally, I'll take the cookie-jar variety over the computer kind any day – the ones with the double-cream filling, for the record.

Brother John Raymond, co-founder of the Monks of Adoration, writes from Venice, Florida.