How private (or public) are Web interactions? - The Tao of Computing - page 328

or networking administrator could track down what you view on
your Web browser. This assumption may not be true—but it also
might be!
And even if your school, company, or ISP does not maintain or
review logs, some of your activities might be inferred by an exami
nation of cookies kept on your computer or in your account—a
topic we discuss next.
What are cookies?
You may have had the experience of going to a Web site for
some work and returning to that site later to discover it seemed to
remember what you did previously. For example, you may have
purchased a book on an ecommerce site. When you went back to
the same ecommerce site a week later, the site may have greeted
you by name or suggested new titles on the same subject as the topic
you purchased. If you bought an airline ticket at a travel site, then
the next visit to the site may have resulted in a highlighting of spe
cial offers originating from the same airport you left the first time.
In each of these cases, the Web site seemed to remember who
you were and what you did previously at that site. Cookies provide
a common mechanism for enabling this type of interaction. More
precisely, a cookie is a small piece of information that a Web site
saves on your computer when you visit the site, and your browser
maintains a list of these cookies. When going to a Web site, your
browser checks this list to determine if a cookie has been placed
there previously by that site. If so, the cookie is sent back to the site
as part of your Web request. With this piece of history, the Web site
may determine something about your past involvement at that
site—either directly from the cookie or by using the cookie's infor
mation to search a database. Altogether, cookies are small pieces of
information stored on your computer that help identify you to spe
cific sites you have visited on the World Wide Web.
As with many records of past history, cookies have potential ad
vantages, but also have an impact on your privacy. On the positive
side, cookies have the potential to streamline and personalize your
interactions with Web sites. By knowing who you are and what you
have done at a site, a Web site can tailor what it displays on its pages
to your preferences and interests. Further, by knowing your identity,