A unique code is used to register a virtual pet or other item using a code that is associated with the pet, and which, when entered, allows viewing and interacting with a virtual representation of the actual item on the website. If the code is entered during a specific time period, it allows obtaining at least one additional item, for example an exclusive item that cannot be obtained in any other way. The specific time period can be extended, e.g., using supplemental codes. The codes may specify fixed or variable time periods, and may be generic extension codes and extend other things other than this period.