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A tiny graphic on a web pages or in an
e-mail message designed to track the behaviour and identity of the person
reading it. Web bugs are gif images 1pixel in size and are transparent rather
than coloured, so they are almost never detected by readers unless they look
at the source code that makes up the page or message. Although they sound
innocuous, these "invisible dots" are powerful tools for advertisers and
website owners. This is because the act of viewing them reveals much useful
information about the person or computer displaying them, in particular the
ip address, the url of the page that was viewed and the type of
browser
being used. Advertising networks use them to build a profile of web surfers
over time, correlating identity information with lists of sites that they
visit, thus helping them to display targeted advertising to web surfers
based on their surfing habits.
Web bugs have more intrusive uses,
particularly in conjunction with html-based e-mail messages. They can tell
the sender if and when the message has been read and how often it is
forwarded, because each viewing of each bug generates a request to the
originating server to send and display the image. They can also be synchronised with
cookies, allowing websites to discover the e-mail identity
of people who visit their sites. One frequently cited example of why this is
a bad idea involves visitors to health sites, who may wish to obtain
information about serious illnesses without being identified. This aspect of
web bug usage upsets privacy campaigners, some of whom have set up
websites to expose offenders. Marketers and advertising networks
predictably claim that the use of web bugs helps web surfers by making it
easier to provide them with useful content and advertising. |
