7. The method of claim 1 further comprising: detecting an occurrence of a first cursor event at the first client system, wherein the detection of the first cursor event includes detecting a location of a cursor at the first display being positioned over a portion of displayed content representing the first specific portion of modified web page content; and causing the first client system to automatically display, in response to detection of the first cursor event, a first pop-up window or layer which includes a first portion of advertising content that is different from the first specific portion of text.
7. The method of claim 1 further comprising: detecting an occurrence of a first cursor event at the first client system, wherein the detection of the first cursor event includes detecting a location of a cursor at the first display being positioned over a portion of displayed content representing the first specific portion of modified web page content; and causing the first client system to automatically display, in response to detection of the first cursor event, a first pop-up window or layer which includes a first portion of advertising content that is different from the first specific portion of text. 15. The method of claim 7 further comprising: identifying at least one advertising campaign topic associated with the first web page; causing a first client system to automatically display a first pop-up window or layer which includes selected advertising content; wherein the displayed advertising content is contextually related to the at least one identified advertising campaign topic associated with the first web page.