In one embodiment, a computer program blocks windows categorized as bad windows, while allowing windows categorized as good windows to be displayed. The computer program may categorize a window by consulting one or more lists. In one embodiment, a list may be updated from time to time to optimize the computer program and prevent program-obsolescence. Techniques for defeating a window-blocking mechanism are also disclosed. In one embodiment, a computer program detects if a window is of a type that offers a product to a user. If so, the computer program provides a separate window containing information regarding the product. In one embodiment, a computer program detects if a user has a need for the computer program. If so, the user is informed of the efficacy of the computer program, which is then offered to the user.