How does internet cookies work

When you request another page from the server, your browser sends the cookie back to the server. These files typically contain information about your visit to the web page, as well as any information you've volunteered, such as your name and interests.

The term "cookie" is an allusion to a Unix program called Fortune Cookie that produces a different message, or fortune, each time it runs. Cookies are most commonly used to track website activity. When you visit some sites, the server gives you a cookie that acts as your identification card. Upon each return visit to that site, your browser passes that cookie back to the server. In this way, a web server can gather information about which web pages are used the most, and which pages are gathering the most repeat hits.

Cookies are also used for online shopping. A name-value pair is simply a named piece of data. It is not a program, and it cannot "do" anything. A Web site can retrieve only the information that it has placed on your machine. It cannot retrieve information from other cookie files, nor any other information from your machine. Sign up for our Newsletter! Mobile Newsletter banner close. Mobile Newsletter chat close. Mobile Newsletter chat dots. Mobile Newsletter chat avatar. Mobile Newsletter chat subscribe.

Prev NEXT. All websites should offer an opt-it pop up for cookies to give you more control over the data you share. If a website does not do this, it is not complying with the GDPR rules and could be fined. On any website, you do not have to accept cookies. You have the option to reject all.

The problem with this is some websites may restrict or block your access to their website. Always check for a padlock symbol, displayed next to the URL address on your browser.

This indicates that the site is secure, meaning your data is protected. Storing lots of cookies can also slow your browser, so reducing the amount you accept in the first place will reduce the impact on your hard drive. You can find out how to delete cookies on different browsers in an article we wrote on the topic. This makes targeting much more precise, and that makes a lot of people uncomfortable.

Different sites have different policies. HowStuffWorks has a strict privacy policy and does not sell or share any personal information about our readers with any third party except in cases where you specifically tell us to do so for example, in an opt-in e-mail program. We do aggregate information together and distribute it.

For example, if a reporter asks me how many visitors HowStuffWorks has or which page on the site is the most popular, we create those aggregate statistics from data in the database. The second is unique to the Internet.

There are certain infrastructure providers that can actually create cookies that are visible on multiple sites. DoubleClick is the most famous example of this. Many companies use DoubleClick to serve ad banners on their sites. DoubleClick can then track your movements across multiple sites.

It can potentially see the search strings that you type into search engines due more to the way some search engines implement their systems, not because anything sinister is intended.

Because it can gather so much information about you from multiple sites, DoubleClick can form very rich profiles. These are still anonymous, but they are rich. DoubleClick then went one step further. By acquiring a company, DoubleClick threatened to link these rich anonymous profiles back to name and address information -- it threatened to personalize them, and then sell the data. That began to look very much like spying to most people, and that is what caused the uproar.

DoubleClick and companies like it are in a unique position to do this sort of thing, because they serve ads on so many sites. Cross-site profiling is not a capability available to individual sites, because cookies are site specific. Revised: November 21, About Us. Why US. Virus Alerts. Refer A Friend.

Site Map. Privacy Policy. Make Payment. Most Internet cookies are incredibly simple, but they are one of those things that have taken on a life of their own. Cookies started receiving tremendous media attention back in February because of Internet privacy concerns, and the debate still rages. Paraphrasing, the definition went like this: Cookies are programs that Web sites put on your hard disk. When I look at the cookie file Amazon has created on my machine, it contains the following: session-id-time amazon.

The data moves in the following manner: If you type the URL of a Web site into your browser, your browser sends a request to the Web site for the page see How Web Servers Work for a discussion. Web sites use cookies in many different ways. Here are some of the most common examples: Sites can accurately determine how many people actually visit the site. It turns out that because of proxy servers , caching , concentrators and so on, the only way for a site to accurately count visitors is to set a cookie with a unique ID for each visitor.

Using cookies, sites can determine: How many visitors arrive How many are new vs. Here's how it works: When you visit HowStuffWorks for the first time, the server creates a unique ID number for you and stores a cookie on your machine containing that ID. For example, on the machine I am using now, this is what I see in the HowStuffWorks cookie file: user www. People often share machines - Any machine that is used in a public area, and many machines used in an office environment or at home, are shared by multiple people.

Let's say that you use a public machine in a library, for example to purchase something from an on-line store. The store will leave a cookie on the machine, and someone could later try to purchase something from the store using your account.

Stores usually post large warnings about this problem, and that is why. Even so, mistakes can happen. For example, I had once used my wife's machine to purchase something from Amazon. Later, she visited Amazon and clicked the "one-click" button, not realizing that it really does allow the purchase of a book in exactly one click.