What are Cookies?

Cookies, more specifically known as "browser cookies", are pieces of data that websites use to store information about you. Unclear definitions of cookies often lead Web users to believe that cookies are dangerous programs that can harvest information from your computer. This is not true! Cookies aren't programs at all—cookies are simply bits of information that help websites serve you better by remembering useful information.

Have you noticed that some website remember what you were doing last? Or, that websites like Gmail and Facebook keep you logged in even after restarting your browser. These capabilites are made possible by cookies. Often, websites use a combination of client-side cookies and server-side data. For example, Amazon will store  a unique login id in a cookie, but it will store your credit card info, shipping addresses, and "shopping cart" in its own database.

There are some vulnerabilities related to cookies, such as session hijacking. Some cookies are used for the information of the website, used to track browsing history to determine which of their pages is most popular.


Different Kinds of Cookies

There are many different kinds of cookies, but they all fit into two categories: session cookies and persistent cookies. Session cookies are not saved onto your computer's hard drive. They have short lifespans, and if the browser is closed, the cookies instantly expire. Persistent cookies are saved onto the your hard drive. On Windows machines, they can usually be found under C:\Program Files\[your browser's name]\cookies. These cookies can be on your hard drive for a long time (default is one year), or you can delete them yourself.

Cookies Used for Advertising

When a website puts a cookie on your hard drive, no other website can read the information in that cookie, making cookies fairly secure. However, if you are visiting a website that hosts advertisements, the advertisements can also put cookies on your computer. If you visit any other sites that have those same advertisements, the ads can use that cookie to "talk" to each other, building a profile of what sites you visit. Even in this scenario, cookies cannot tell any website your name or email address, but ad companies (such as doubleClick) will learn what products you might be interested in buying. The result is that the company will send you tailor-made advertisements that appeal to your specific interests.

Concerns for Parents

  • Cookies can pose a security threat when you use a computer that many people have access to. If you make an online purchase or create an account on a public computer, the next user to come along could buy things with your credit card information, since your personal info has been saved onto a cookie on that computer.
  • In view of the potential security risks, some computer users may think that disabling cookies altogether is a good idea. However, disabling cookies on your computer will cause problems as you surf the Web, since many websites won't function properly without cookies.

How Can I Stay Safe?

Generally, any website that you can trust with your information will also be conscious of what it stores in cookies on your computer, so as long as you are only giving personal information to repudable sites, you won't have problem.

  • By far the biggest risk is leaving cookies on a public computer. Avoid making purchases or giving out sensitive information on public computers. Always log out of any accounts. If possible, only make purchases and create Web accounts on your home computer.
  • Be aware of what cookies your computer is storing. The links below offer step-by-step instructions that detail how you can set up cookie preference settings on your home computer.
  • When you are done using a public computer, you should delete any identifying information so that other people can't take advantage of it. You can delete all information from your Web browsing session simply in all of the leading Web browsers.
    • In Firefox click on Tools and then click on Clear Private Data. From the drop down menu select Everything. If you don't see any details, Click on the Down Arrow button by details. Check all of the boxes and click Clear Now.
    • In Internet Explorer go to Safety > Delete Browsing History and then select all of the boxes.
    • In Google Chrome click on wrench icon () or the menu button (); click Tools and then Clear Browsing Data. Select beginning of time from the drop down menu, check all of the boxes, and click Clear browsing data.
    • In Safari go to the Safari menu, click Preferences; then click Privacy and click Remove All Website Data.
  • Additionally, some browsers provide a mechanism for temporarily disabling cookies and browser history. In Chrome this is called "incognito mode" and is accessible by pressing Ctrl-Shift-N. Some parents may wish to disable this mode, as it does not save browser history. See: How to Disable Incognito Mode in Chrome

Flash Cookies

Flash cookies are specific to the Flash runtime and are stored differently from normal, browser-based cookies. They require special attention since they exist under the radar of browsers, and may still exist when the user deletes browser cookies.

Where Can I Learn More?

How to Check Cookies in Chrome

How to Check Cookies in Firefox

How to Check Cookies in Internet Explorer

How to Check Cookies in Opera

How to Check Cookies in Safari

Visit this page for help setting cookie preferences on you iPad, iPhone, or iPod touch.

Read the HowStuffWorks article to learn even more about Internet cookies.

Find recent cookie news or answers to frequently asked questions at Cookie Central.