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HTTP cookie

A HTTP cookie (usually called simply a cookie) is a packet of information sent by an server to a World Wide Web browser and then sent back by the browser each time it accesses that server. They were invented by Lou Montulli, a former employee of Netscape Communications.

Table of contents
1 Purpose
2 Opposition to cookies


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.

Opposition to cookies

Some people are opposed to the use of cookies on the Web. Below are some of their reasons.

Inaccurate identification

Perhaps the most fundamental objection is that cookies don't identify a person, but merely a web browser. For example, they do not differentiate between multiple users who share a user account. Also, a single person who uses multiple computers will have a distinct set of cookies on each of those computers.

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.

This article (or an earlier version of it) contains material from FOLDOC, used with permission.