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What are Computer Cookies?

By R. Kayne
Updated May 17, 2024
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A computer cookie, also referred to as an "HTTP cookie," is a small text file that contains a unique ID tag, placed on the user's computer by a website. In this file, various information can be stored, from pages visited on the site, to information voluntarily given to the site. These tiny files provide practical benefits to both users and website operators, and generally make surfing the net a smoother experience than it otherwise would be. Nevertheless, privacy advocates tend to be wary of them, since many users are unaware of exactly what information is collected, and how the information may be used or shared.

Types of Cookies

There are two types of computer cookies: temporary and permanent. Temporary cookies, also called session cookies, are stored for a short time and then removed as soon as the browser is closed. Permanent cookies, also called persistent cookies, are stored for a long time on the user's hard drive and, if deleted, will be replaced the next time the respective site is visited.

The temporary cookie is very simple. It works by setting aside a little bit of browser cache memory to retain information about a user's activities during his visit. After putting a selected purchase in a shopping cart, for example, the user might continue to search the site for additional products without having to go through a separate checkout for each item. Once the browser is closed, however, all temporary cookies are lost. Return surfers are not recognized, shopping carts are empty, and any other forms or information will have to be provided again.

By contrast, permanent cookies make it possible for a site to recognize a surfer on a continuous basis. This is accomplished by transferring a text file with a unique ID tag to the visitor's hard disk, while maintaining a matching file on the server. On subsequent visits, the browser automatically hands this cookie over, allowing the site to instantly pull up the matching file. Persistent cookies can exist for years, unless deleted, or until the cookie's internally defined lifetime has passed. Today, permanent cookies are the most common type of cookie used.

How Cookies Are Used

At their most basic level, a website uses computer cookies to log when an individual visits, which pages are viewed, and how long the visitor stays. If he or she returns at a later date, the visitor’s cookie triggers the log of previous visits, and amends it to include what happened during the new visit. If personal information is offered on any of these visits, it is instantly associated with the "anonymous" ID tag, and consequently, the entire profile. In this way, a site can more easily monitor changing trends and other statistics among its visitors. Over time, permanent cookies have also resulted in some initially unanticipated uses, such as web profiling.

Marketers have developed a substantially broader application for cookie profiling. Having advertising rights on many of the most popular websites, marketers can now pass third-party cookies to surfers. This allows them to recognize individuals as they travel between different sites, logging comprehensive profiles of people's surfing habits over a period of months, or even years. Sophisticated profiling programs quickly sort the information provided by computer cookies, categorizing targets in several different areas based on statistical data. Age, income level, and even sexual orientation can often be determined with varying degrees of accuracy through cookie profiling, along with many other characteristics. Much depends on how much a person surfs, and where he or she chooses to go online.

As a result of public outcry in response to hidden profiling, cookie controls are now included in web browsers to allow users to turn cookies off — options that were not available in 1995 when permanent cookie technology was first introduced. Cookie controls also allow user-created lists for exceptions, so that a user can turn most cookies off, for example, but allow them from sites where computer cookies are put to a desired purpose. Third-party cookies often have their own controls, as they are normally placed by marketers.

Origin

As a concept, the computer cookie dates back to 1994. In that year, it was adapted as a tool for the World Wide Web by Leo Montulli from a similar technique, called "magic cookie," which was used in UNIX® systems. This is also the origin of the term itself. It was not for another couple of years, however, that the cookies became widely known to the general public. In 1996, articles about them began appearing in the mainstream press, many of which raised concerns about privacy, and in turn inspired the changes in web browsers that ultimately gave users more control over how cookies were implemented on their individual machines.

Are Cookies Dangerous?

In and of themselves, computer cookies are not malicious; they generally make surfing more seamless, and help websites operate more profitably and with greater efficiency. There are legitimate concerns, however, about the ways that cookies can be used to follow users from one site to another, forming comprehensive profiles. Some consider this to be a violation of privacy, and in the wrong hands the information can potentially be exploited for questionable purposes. Much akin to managing the privacy settings on social networking sites, however, each user has the power to decide for himself whether to accept cookies, whether to block certain types, and how often to purge them. Most modern browsers, as well as many Internet security products, give users easy and flexible control over all of these decisions. Many websites detail their cookie process, if any, in their privacy policy.

WiseGeek is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Discussion Comments
By anon281117 — On Jul 22, 2012

I always have cookies popping up on my computer. What should I do?

By anon267708 — On May 11, 2012

@Anon 244109- Post 45: To the best of my knowledge cookies of websites one never visited can also be stored in a user's computer.

It is done by camouflage methods.

Suppose you visit a religious site, but that site is actually a front to a "dirty" site, either distributing malware or pornography without even so much as mentioning the word "malware" and "pornography" on the religious site.

So, when you visit such a site, then cookies of the actual "dirty" sites can be transferred and installed in your computer.

That is how Trojans and other malware/viruses/etc. are also stored.

Give your husband the benefit of the doubt. It is not only about visiting some "unwelcome" sites.

You may also want to strengthen your bond. So, if you tell him that you trust him that will strengthen your bond. Best wishes.

By anon244109 — On Jan 31, 2012

I would like to know if your computer can store cookies for websites you have never visited. I am seeing suspicious website on my husband's computer, but he insists he's never been to those sites. Is that possible?

By anon142482 — On Jan 13, 2011

Good article, I didn't fully understand cookies until now. Just a note for anyone: you can turn on a "private browsing" setting on your browser, so no cookies are stored on your hard drive. It may be a bit slower since you have to load the page every time you enter it, but its much safer. Also, a good anti-virus program like norton will pick up these cookies and give you an option to keep or delete them. Personally, I keep the private browsing setting on, and scan just to be sure.

Anon54973 had a good comment. The best way is to control your online habits. Be wary of everything, you can never be to sure who's watching and waiting, some say "ah they won't attack me, what could I have that they would want" but it doesn't matter. If you don't have anything of value to them, they can use your computer for their "botnet" -- and use your computer with a large number of other computers to attack people's computers, websites, or even government servers. Don't trust anything on the internet. Be careful what you click.

By Adam Asad — On Dec 05, 2010

This article is very good and defines very well what are computer cookies: The sites that we have visited on the internet are stored in our browser that sites are called cookies.

By anon107280 — On Aug 29, 2010

How do I know what cookies are in my PC?

By anon100596 — On Jul 30, 2010

when I sign out of my e-mail account, I get a message saying I'm signed out of the e-mail account services but say they can't sign me out of another site. Then they say I need to clear the browser cookies and then close all browser windows. What are they talking about?

By anon91280 — On Jun 21, 2010

"Cookie contents are encrypted and are only readable by the site that placed them."

This is not true.

Cookies can be encrypted but most cookies are not.

By anon87136 — On May 28, 2010

There are also files that Macromedia and Sun Java store on your computer. These files are not browser dependent.

By anon87059 — On May 27, 2010

i thought cookies were something you ate for a dessert until someone told me differently. Once I was looking to purchase some lingerie online and I noticed that it linked me to hustler as in Hustler magazine!

Never went there but scary to think that it may have stored something on my computer that made it look as thought i may have. What to do?

By anon80793 — On Apr 28, 2010

That was a great, easy to understand article. I knew what cookies did but not how or why. Thanks

By anvai — On Apr 20, 2010

To anon67978: that happened to my computer as well, and what i did was i deleted all the cookies and plus those website links stored in your favorites bar tab. Because I entered their website and they blocked my access by placing an advertisement in front of my screen, asking me to purchase their anti-virus but i didn't as i know i got more than one anti-virus.

Or if you don't know what I'm talking about use your anti-virus to scan your computer before moving on.

By anon69150 — On Mar 06, 2010

I usually use a site to see my son's grades but since some months ago when i try to log in it says

"Your browser either does not support cookies,

or you are not accessing this site via its

fully qualified domain name. Please enable

cookies for this domain and try again." What can I do?

By anon67978 — On Feb 28, 2010

I recently signed up for an affiliate marketing website. It seems as if they took over my computer. They must be a scam because I looked them up and seemed legit until I was digging a little deeper. They were more worried about getting more money from my credit card than helping me with my "site they provide".

Since protecting my computer again, it is trying to get attacked one after the other. Should I block all cookies? Is there anything you can tell me to do? Thanks for all your great info about this.

By anon63041 — On Jan 30, 2010

Seeing all the problems faced due to cookies, it always seems to be better to revert to our olden days usage of doing the things by physically reaching the concerned places/shops, etc. The computer operation has already made the human being so lazy, that even for stuffing the food inside the mouth. man-kind may ask the computers to make suggestions

Please wake up, at least now and do things by physical hard work so that cookie like things don't eat away your time, money etc.

By anon54973 — On Dec 03, 2009

cookies could be helpful, but only if they come from legitimate sites. (what i mean by legitimate websites is websites that you frequently visit and you know are legal such as your banking website.) Now cookies can also be harmful if they are used to steal information from you without your consent. this usually happens when you visit a "bogus" online shops. they can use the information they get from you from the "cookies" to send you some unsolicited advertisements on your e-mail and other hackers can even use the information they got from you through the use of these cookies to send your computer a "pop-up" virus or a kind of spyware that will bombard you with advertisement pop-ups each time you turn on your computer and this could happen even if your not browsing the web or using your internet explorer.

so the best defense still, is control your internet habits. - Seifer5 Philippines

By anon43318 — On Aug 27, 2009

I have paid membership to an online site. Why can I not access them without cookies? They accepted my payment without the cookies.

By sachxn — On Aug 26, 2009

great article. also see how to test cookies.

By cascas21 — On Jul 22, 2009

can you get a virus with cookies?

By anon37753 — On Jul 21, 2009

what happens when you get rid of your computer's cookies?

By anon35460 — On Jul 05, 2009

Yeah! I never learned computer formally, only the my English language that enables me to understand the terminology of the computer, like cookies, for example. Thanks for your nice and understandable article, from which I can get the idea what is the function of cookies and why they need to be cleared always, from our internet programs(or something like that)

By anon32654 — On May 25, 2009

How do you enable your web cookies in order to create an account that needs the person to have cookies enabled? Like for example: I want to create an account in Code Wiki and it requires that I must have my cookies enabled in order to create an account.

By anon32143 — On May 17, 2009

Hi *is* there some setting so i don't get cookies?

By anon25456 — On Jan 29, 2009

If I have paid membership in Blue Mountain, why can I not access them without cookies? They accepted my payment without cookies.

By anon25213 — On Jan 25, 2009

I now know what cookies are but I have this problem where recently when I want to go to google mail it won't go but before it got there quickly. Is that because of my cookies?

By anon24952 — On Jan 21, 2009

Can I drink them with milk?

By anon22037 — On Nov 26, 2008

Hi,

I would like to ask you all a question. Does a cookie only come through internet usage or can it be placed in your computer by some one to track your internet usage.

By anon21437 — On Nov 16, 2008

Can cookies be placed on your computer after it is shut off? Thanks.

By anon10717 — On Apr 01, 2008

Very Good. My husband has been trying to teach me about them for years and I just couldn't understand. Thanks a lot. No I'm also cognisant of what exactly happens with my information as I move across the net. I have one question though - Do you have information on whether cookies breach our privacy?

Carolin

By anon7051 — On Jan 16, 2008

Many shopping carts do not require a visitor to login, so the cookie itself contains the selected items without any necessity for the cart to maintain a complimentary file. When the visitor is ready to checkout, even after several days or weeks, the cookie is read and the selected items are displayed for the visitor. In other words the cookie is the visitor's cart.

By anon5425 — On Nov 25, 2007

Can I change my cookies or something to undo the block on a particular website? Is my ID tag being read when I try and post an ad?

By anon3878 — On Sep 21, 2007

Wow gr8 explaining bout the cookies and various other things! So simple and all for a person like me! You see im not that great on computers and all but that was really gr8 explaing

but id like to ask, when i do a scan with avg or spybot only a few problems pop up after these scans have finished...

But then i just did a scan with adaware and 380 (infections popped up on the scan summary)

although they did not come under the critical heading. They came under as privacy ?Im not sure what that means anyhow that's not my question, my question is i deleted all 380 of them because i wanted my system clear? Did i do wrong by deleting them? Like did i harm my comp in any way?How come they showed up in adaware and not the other 2 scans?

By anon1414 — On May 29, 2007

if cookies are good then why do certain sites such as yahoo mail send error messages saying to clear cookies and try again?

By anon625 — On Apr 30, 2007

Thank you for your informative site on what "cookies" are. I teach technology to 4th through 6th graders and am trying to broaden their knowledge of marketing techniques used by internet marketers. We are doing an activity that asks students to be able to identify when a site has placed a cookie on the user's computer. How can one tell if a cookie has been placed on your computer? All I can show them is that the next time the user visits that site it is able to "greet" the user and has knowledge about the user. Is their an "easy" way to tell if a cookie has been placed on your computer after visiting a site?

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