Functionality creep is what occurs when an item, process, or procedure designed for a specific purpose ends up serving another purpose for which it was never planned to perform.

Example

In the United States, when the Social Security system was created in the early 20th century, each worker was issued a unique, nine digit, Social Security number (SSN). These SSNs were created to keep track of a person's contributions to the Social Security System and to determine his eligibility for benefits.

Due to functionality creep, the fact that each person has a unique SSN has led to them becoming a de facto identification number for each person. SSNs are now requested for other non-Social Security related government functions, such as income tax filing and passport issuance, plus many more non-government functions such as tracking credit history, employee ID numbers, and school records. Early Social Security cards, in fact, had printed on them "Not to be used for identification," a notice which was removed from later editions of the card.

See also

• Creeping featurism, when a computer program ends up doing more and more.