A form of text-based online advertising, double-underlined links are ad media that are meant to be relevant and unobtrusive. The way it works is this: the double-underlined links scan each page for appropriate keywords and contextual relevancy. The keywords are pre-chosen by the online publisher to be relevant to the site, however, more often than not, they appear due to supply and demand. If a match is found, a clearly visible advertising link (usually indicated by a green or blue double underline) is auto-generated. When you hover your mouse over this type of link, a small pop-up box will appear with the sponsored ad information in it. If you don't "scroll over" or click on a link, your reading experience is uninterrupted.
Double-underlined links make use of server-side technology, meaning it resides within the online publisher's Web site. This is meaningful because unlike cookies, no code or information is passed to your computer, and therefore it does not compromise your privacy. If you use a browser prior to Internet Explorer 5.0, Netscape 7.2, or Firefox 0.8 or later, you won't see double-underlined links.