Nagware is a software utility that adds users into upgrading or buying a premium version of software by sending constant pop-up messages or notifications.   It is a marketing tactic used by software developers in order to remind users to take advantage of special offers and purchase software. Nagware is also known as begware , annoyware , nagscreen and guiltware . It is built into commercial software that periodically prompts the user to register the product. Nagware is commonly used with  shareware  programs which have been downloaded for trial use. It keeps the message up for a certain time period, forcing the user to continue using the program.