A Web Bug is a single pixel graphic embedded in a Web page or an HTML email message. Being a single pixel makes the graphic virtually invisible to the viewer. How does the Web Bug work? By using a cookie...
What are Web Bugs used for?
While companies may be quick to maintain that they gather only "non personally identifiable information" this is not the whole story. If you have provided personal details, say via a "survey", then these details will be aggregated, stored and used.
HTML Email can be affected web bugs and malicious scripting in the same way as a WWW page. They can be used in a variety of ways... by spammers to test for active email accounts or to comprimise your machine directly via a security problem in the operating system.
An embeded script or web bug is invisible to anyone reading the message but can be easily detected by looking at the source code of the message.
To guard against this form of intrusion you can...