Restrictions can be applied at various levels: a government can apply them nationwide, an ISP can apply them to its clients, an employer to its personnel, a school to its teachers and/or students, a library to its patrons and/or staff, a parent to a child's computer or computer account or an individual to his or her own computer.
The software is designed to control what content may or may not be viewed by a reader, especially when used to restrict material delivered over the Internet via the Web, e-mail, or other means.