1. Generally, any means (technical, operational, or managerial) for keeping private the information contained in data that are transmitted, stored, or processed in a computer system. A data security system must make information available to those authorized to receive it, without undue delay or inefficiency. Also, it must keep information secret from those not so authorized, in such a way that the cost of unauthorized disclosure would exceed the value of the information to the illegitimate recipient.

A data security system may involve physical security (safes, locks, entry cards) for access to disks and passwords, and also the techniques of cryptography and authentication. The specification and design of a good data security system relies on the formation of an appropriate threat model. See also security.

2. A system for ensuring the integrity and longevity of stored data, usually involving regular copying and storage in a remote location. See also backup.