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 not intended.

=Example=

In the United States, when the Social Security (United States) system was created in the early 20th century, each worker was issued a unique, nine digit, Social Security number (SSN). These SSNs were created for the sole purpose of keeping 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 them be misused as a de facto identification number for each person. SSNs are often requested for other non-Social Security related government functions, such as income tax filing and passport issuance, as well as some non-government functions such as tracking credit history, employee ID numbers, and school records.

SSNs are not supposed to be used for the purpose of identification. Early Social Security cards, in fact, had a notice printed on them Not to be used for identification . The notice is not printed on later editions of the card but it is still valid. Following a number of security breaches of administrative and school computers resulting in large-scale identity theft in 2005 a bill has been proposed which makes the use of SSNs as identifiers of students illegal.

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