The dark side of the web - The Computing Universe: A Journey through a Revolution - page 260

Fig. 12.18. Third-party cookies allow
tracking companies and ad brokers to
track the browsing behavior of web
users. The green circles are the websites
visited by a user and the purple circles
are the companies analyzing the user's
behavior and selling the information to
the red sites that serve targeted adver-
tisements to the user.

page this may contain an advertisement linking back to a different website.
This site sets a cookie that tells the ad broker service that the user clicked on
this web page. When the user visits another website the same thing happens
and another cookie is downloaded. In this way, an ad broker can build up a
complete picture of the user's browsing history. This information can then
be sold to advertising agencies that can generate targeted, personalized ads,
specific to the interests of the user, as revealed by their browsing history.
Spyware is software that can hide itself on a computer and gather and
transmit information back to a black hat without the owner's knowledge.
Spyware is different from viruses or worms in that the software does not try to
replicate itself or spread to other computers. The Trojan horse software used
by the Berkeley hacker is a form of spyware, for collecting user login infor-
mation. Spyware can also collect other types of data such as bank and credit
card information. In addition, spyware can track the user's Internet activity
and serve annoying pop-up ads or change the computer's security settings and
disable antivirus software. Cookies are a form of spyware and antispyware soft-
ware now usually reports the presence of third-party cookies and offers ways
to remove them.
Cookies have serious implications for the privacy of Internet users. In
2000, the U.S. government established strict rules for setting cookies, and mod-
ern browsers now offer users the option to block all cookies. In its Directive on
Privacy and Electronic Communications in 2002, the European Union introduced a
policy requiring a user's consent for setting cookies. It stipulated that storing
data on a user's computer can only be done if the user is provided with infor-
mation about how this data will be used. This was later relaxed to exempt
first-party cookies - as in virtual shopping carts - from this requirement of
obtaining prior user consent.

Key concepts

Buffer overflow M

Trojans, viruses, and worms M