What is a Cookie?

Cookies are small files that are stored on your computer upon visiting a website. The cookie holds a very small amount of information that allows the website to recognize your computer and then deliver a page that is tailored to you, improving your experience. Sometimes the information in the cookie is shared with a related site so that site can also customize your experience.

The cookie itself does not contain your usernames and passwords or any personal identifying information. It contains data that allows a server to access information you have provided. The content of the cookie is very simple:

  • The name of the server the cookie was sent from.

  • The lifetime of the cookie (how long it will stay active).

  • A value - usually a randomly generated unique number. The website server that sent the cookie uses this number to recognize you when you return to a site or browse from page to page. Only the server that sent a cookie can read, and therefore use, that cookie.

Examples of cookies in action

  • You visit a site and it remembers your login information.

  • You visit a site that allows you to pick a “theme” like colors or background. When you return to the site, it remembers your theme.

  • You start to fill out a form but have to click back to another page before you have finished. When you come back, the form information is still there.

  • Products you were browsing on a different web page show up in advertising blocks on the page you are viewing now.

Why are cookies used?

  • They improve your experience by allowing the website to access your login information and preferences, so you don’t have to enter that information every time you visit.

  • They reduce the load on the website’s data server. They are important for websites that store huge amounts of data, require logins, and offer customizable features.

  • Increasingly they are used for marketing and tracking purposes, such as tracking products you have viewed and then showing that product again on another page. Some people consider this a violation of privacy. More on tracking cookies below.

Cookie types

There are two types of cookies: session cookies and persistent cookies.

  1. Session cookies are created temporarily and are deleted once you close your browser window.

  2. Persistent cookie files remain on your computer (in the browser subfolder) and are activated again when you visit the site that created the cookie. This type of cookie remains active for the duration set in the cookie file.

Are cookies secure?

Cookies alone are not a threat to security. They are only used to store a small amount of information that a server can use to access information that you have actually volunteered. When you are providing information to a website, always ask yourself if the information should be treated confidentially and question whether you should be providing that information online at all.

Cookies usually cannot be used to reveal your identity or personally identifying information. However, they are being used more heavily for online marketing and can be used to create a profile of your surfing habits.

What are Tracking Cookies?

Some websites embed advertising on their pages that is served from a third party site. It is possible that those advertisements can store a cookie on your computer that then allows that third-party site to access information, such as the particular products you viewed, pages visited, etc. When you visit another site that contains a similar advertisement from the same third-party site, the advertiser can read the cookie and use it to understand your browsing history. The idea is that the advertisements they show will be more relevant to your interests. Many people consider this an invasion of privacy because it allows advertisers to build up a user profile without the user giving consent.

How to enable/disable cookies on Mac

There may be times when you want to either enable or disable cookies on your Mac. Before you disable cookies, however, keep in mind that certain websites actually require them in order to function properly. Disabling cookies may prevent you from experiencing the full features of the site or prevent you from accessing it entirely. Keep this link handy for a quick way to enable cookies in Safari, Firefox, or Chrome on your Mac:


We hope this clears up some of the mystique around cookies and just what they are doing (or are not doing) on your computer!