Registered users normally provide some sort of credentials (such as a username or e-mail address, and a password) to the system in order to prove their identity: this is known as logging in.
The system may also allow a logged-in user to send and receive messages, and to view and modify personal files or other information.
[citation needed] The subject of systems' transparency in this regard is one of ongoing debate.
[citation needed] Registration may be seen as an annoyance or hindrance,[2] especially if it is not inherently necessary or important (for example, in the context of a search engine) or if the system repeatedly prompts users to register.
A system's registration process might also be time-consuming or require that the user provide the information they might be reluctant to, such as a home address or social security number.