What is a Cookie?
Cookies were introduced to Internet browsing by the pioneering firm Netscape.The name “cookie” was a term already in use in computer science for describing a piece of data held by an intermediary.
Internet cookies are small pieces of information in text format that are downloaded to your computer when you visit many Web sites. The cookie may come from the Web site itself or from the providers of the advertising banners or other graphics that make up a Web page. Thus visiting a single Web site can actually result in the downloading of multiple cookies, each from a different source. You may never actually visit a page of one of the major advertising agencies like Doubleclick.com but you will still get cookies from them. Cookies typically contain some kind of ID number, a domain that the cookie is valid for, and an expiration date. They may also contain other tracking information such as login names and pages visited.
There are a number of cookie viewers available, which will also give some information about the meaning of the content. A good freeware program is Karen’s Cookie Viewer by the well-known programmer, Karen Kenworthy. A cookie viewer is also available in the utility program WinPatrol. These programs can be used to delete selected cookies.
Where are Cookies Kept?
There is no one specific location for cookies. Every browser has its own way of storing cookies. Not only the location but also the format of the cookie storage varies from browser to browser.
Internet Explorer uses an individual text file for each cookie in a folder called “Cookies”. The location of the folder varies in different versions of IE and Windows. Each user account has its own cookies. The easiest way to find the cookie folder is to enter “cookies” in the Start-Run line of Windows XP or to enter “shell:cookies” in the Start search line for Vista/7.
Firefox formerly used a single text file for all cookies but starting with version 3.0 switched to an SQLite database. The location is in %AppData%\Mozilla\FireFox\Profiles\
Google Chrome also uses an SQLite database.
What are Cookies for?
They are necessary to provide the function of “persistence”. Browsing the Internet involves what is known as a “stateless” process. In other words, a Web site ordinarily has no memory of who comes and goes. (Actually, logs of traffic are kept but these are not involved here.) As soon as the information that your browser requests from a site is downloaded to your computer, the connection is dropped. If you return to the site a minute later (or whenever), the site has no knowledge that you were just there. If a site has several pages and you go from one to the other the site does not remember which pages you have been to. That is, it won’t unless a cookie is on your machine to remind the site and provide continuity.
Cookies can provide account information so that you do not have to continually sign in to sites like Yahoo or Amazon. This can obviously be useful but it raises privacy questions.
Cookies and Privacy
Although some cookies provide a useful function, many others may not be desirable. As the Internet has evolved from its beginnings in academia and government to a commercial enterprise, cookies have inevitably been turned into a tracking mechanism used by advertisers. In principle, cookies are only accessible to the site that originated them but large advertising agencies with many clients can easily circumvent this restriction by collecting information for all their clients under one domain. A fairly harmless (and perhaps even useful) advertising application of cookies is to rotate banner ads as you go from page to page to make sure that you do not see the same ads over and over. However, there are more invasive tracking methods that might involve cookies and therein arise privacy issues.
It should be emphasized that cookies are plain text files and, as such, are not executable programs and cannot do anything to your computer.