UICs Are Not Necessarily Unique

It is important to note that a UIC does not necessarily identify one particular user. It is possible for the system manager to assign the same UIC to two or more user accounts. It is also possible to reuse a UIC previously assigned to a user account that has been deleted.

Because UICs are closely related to file protection, most system managers ensure that no two current users share the same UIC, and many avoid reusing an old UIC. Sharing of UICs can also cause confusion with identifiers (described later) and allow one user to view the private files of another with whom he or she shares a UIC. Further, if a malicious user were to damage the system, but shared a UIC with other users, it might be difficult, or impossible, to determine which user was responsible.

Of course, a system manager may find valid reasons for violating either of these guidelines on a case-by-case basis.