Also called a "Web beacon," "pixel tag," "clear GIF" and "invisible GIF," it is a method for passing information from the user's computer to a third party Web site. Used in conjunction with cookies, Web bugs enable information to be gathered and tracked in the stateless environment of the Internet. The Web bug is typically a one-pixel, transparent GIF image, although it can be a visible image as well. As the HTML code for the Web bug points to a site to retrieve the image, it can pass along information at the same time.
Web bugs can be placed into an HTML page used for e-mail messages as most mail programs support the display of HTML pages. See e-mail tracker, cookie, state and anonymous proxy.
There are a myriad of ways in which Web bugs can be used. This example uses a third-party tracking site to determine how much merchandise was purchased for a particular banner ad campaign. In scenarios such as these, the individual users may still remain anonymous, even though their buying habits are disclosed.
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