Q: What is a “cookie”?

A: A cookie is a piece of information that a website you visit can store on your computer, to be retrieved the next time you visit that website.

Q: What are cookies used for?

A: Cookies hold any information the website designer wants to be able to remember about you, the next time you visit.

One common use of cookies is to hold customization preferences. Many websites allow you to change the way they look or act; these settings are usually stored on your computer in a cookie. One example of this is the volume setting on a YouTube video.

Another use of cookies is to store identity information. Some sites that require a login have a checkbox marked something like “remember me”. If you check the box, then identifying information (perhaps your login ID) is stored in a cookie.

Yet another use of cookies is tracking your behavior, for advertising purposes. A cookie might hold a record of whatever you do or look at on a website. Then the website can use the cookie to determine what advertisements to show you.

Q: Which applications store cookies?

The main applications that store cookies are web browsers (e.g., Internet Explorer, Firefox, Safari, Opera, Chrome), and Adobe’s Flash Player, which runs Flash (e.g., YouTube videos, many games, etc.) inside the web browser window.

Q: Can a cookie mess up my computer, like a virus?

A: No. A cookie is just a piece of information that a website or a person can look at. By themselves, cookies do not do anything.

Q: Are cookies a problem?

A: Sometimes. But you can do something about this problem.

Many cookies pose no problem at all. For example, if you customize a website, then you will probably be happy to have your preferences stored on your computer.

On the other hand, the fact that companies can and do store any information about you that they they want, and the fact that they do so on your computer, is troubling for some people.

Another issue is that your computer might hold information that would lead to trouble if other people found it. There are many good reasons to hide information; for example, the activities of some political activists, the trade secrets of businesses, and the plans of military units may all need to be kept secret. If not managed properly, cookies might be a way to find out some of this information.

Fortunately, modern web browsers offer effective tools for managing cookies. Most of them let you view the cookies on your computer, eliminate the ones you do not want, and set policies about when cookies can be stored and how long they are kept. Some browsers now offer a “private mode”, in which cookies are not stored at all.

Thus, today, cookies stored by a web browser rarely present a problem. But then there are Flash cookies ....

Q: Are Flash cookies especially problematic?

A: Unfortunately, yes.

As noted above, modern browsers include cookie-management tools. However, this has nothing to do with Adobe Flash, which stores its cookies separately. When you view your browser’s cookies, you do not see the Flash cookies. If you tell your browser to delete all cookies, then the Flash cookies are still there. And in your browser’s private mode, Flash does not stop storing its cookies.

The result is that many people, even some who are very serious about privacy, do not even know that Flash cookies exist. This site is an attempt to get the word out.

Q: What can I do about unwanted Flash cookies?

A: Go back to the main page, and either check out the Adobe Flash Player Settings Manager, or else read one of the other articles, and then try the Settings Manager.

Happy cookie flushing!

Posted: 19 Aug 2009. Last edit: 28 Aug 2009.