17. The system of claim 15 , wherein executing the first application program in response to detecting selection of the electronic message includes displaying an object on the display.
15. A computer system, comprising one or more processors; and memory for storing a computer program for execution by the one or more processors, the computer program including instructions for: receiving an electronic message that is sent over a network, the electronic message including a body of text including one or more words to be displayed to a receiving user, and a first portion of a first application program, the first application program including functionality for displaying advertisements on the display; after receiving the electronic message, detecting selection of the electronic message; and, in response to detecting selection of the electronic message: opening the electronic message, displaying the body of text on the display, and executing the first portion of the first application program, which calls a second portion of the first application program using as a parameter at least a portion of the one or more words displayed to the receiving user, the second portion of the first application program being located at a site on the network that is remote from the computer system, thereby retrieving an advertisement and displaying the advertisement on the display.