HTTP cookie

Table of contents

1 Purpose 2 Permission 2.1 Internet Explorer 2.2 Mozilla Firefox 3 Permanence 4 Identification 5 Opposition to cookies 5.3 Inaccurate identification 5.4 Privacy, anonymity and advertising

Purpose

Cookies can contain any arbitrary information the server chooses and are used to maintain state between otherwise stateless HTTP transactions. Typically this is used to authenticate or identify a registered user of a web site without requiring them to sign in again every time they access that site. Other uses are maintaining a "shopping basket" of goods selected for purchase during a session at a site, site personalisation (presenting different pages to different users), and tracking a particular user's access to a site.

Permission

A browser may or may not allow the use of cookies. The user can usually choose a setting.

Internet Explorer

Tools > Internet Options > Privacy Tab

• Use slider to set options, or use advanced options

Identification

If more than one browser is used on a computer, each has a separate storage area for cookies. Hence cookies do not identify a person, but a combination of a computer and a web browser. Thus, a single person who uses multiple browsers and/or computers will have a distinct set of cookies for each computer/browser combination. On the other hand, cookies do not differentiate between multiple users who share a computer and browser.

Inaccurate identification

See above.

Privacy, anonymity and advertising

Cookies also have some important implications with respect to a user's privacy and anonymity on the web. One way is that some companies monitor users' visits to disparate web sites for marketing purposes. Some sites contain images called web bugs (that are transparent and only one pixel in size, so that they are not visible) that place cookies on all computers that access them. E-commerce websites can then read those cookies, find out what websites placed them, and send e-mail spam advertisements for products related to those websites.

Companies that use this system defend it as an effective way to give consumers access to products in which they are likely to be interested. If sites that place these tracking cookies are paid by the commercial operator, the revenue can allow them to place their content online at no cost to the creators.