We use the term security in many ways in our daily lives. A security system protects our house, warning the neighbors or the police if an unauthorized intruder tries to get in. Financial security involves a set of investments that are adequately funded: When we talk about computer security we mean that we are addressing three very important aspects of any computer related system- Confidentiality, integrity, and availability.

Confidentiality: It ensures that computer-related assets are accessed only by authorized parties. That is only those who should have access to something will actually get that access. By access we mean not only reading but also viewing, printing, or simply knowing that a particular asset exists. Confidentiality is sometimes called secrecy or privacy.

Integrity: It means that assets can be modified only by authorized parties or only in authorized ways. In this context modification includes writing, changing, changing status, deleting and creating.

Availability: Availability means that assets are accessible to authorized parties at appropriate times. In other words if some person or system has legitimate access to a particular set of objects, that access should not be prevented. For this reason availability is sometimes known by its opposite, denial of service.