Computer security is the process, procedures, or tools which assure that data entered into a computer today will be retrievable at a later time by, and only by, those authorized to do so. The procedures should additionally include systems by which computer system managers will be notified when attempts at penetrating security are made.
Security is violated when some person or persons succeeds in retrieving data without authorization.
Security is also breached when someone manages to destroy or altering data belonging to others, making retrieval of the original data impossible. Security is closely related to the more general topic of how to obtain a dependable computing system. Dependability is the trustworthiness of a system and can be seen as the quality of the service a system offers. Integrating security and dependability can be done in various ways. One approach is to treat security as one characteristic of dependability on the same level as availability, reliability and safety.