The practise of deliberatly breaking the trial version of a piece of shareware to encourage users to buy a copy. This normally takes the form of a trial period, after which the program will refuse to start, but occasionally programmers come up with more subtle annoyances. The trick is to ensure that the product is usable for testing, but to ensure that the end user is well aware that they should be paying for a copy if they intend to keep hold of it.
Some of the most popular shareware avoids this idea.