The document discusses computer intrusion and data security. It defines intrusion as someone unwanted gaining access where they are not invited. In computing, intrusions can exploit system weaknesses to collect or access data without authorization. Data security aims to protect digital privacy and prevent unauthorized access. Various types of attacks that threaten data security are discussed such as interruption, interception, modification, and fabrication. The document also outlines security mechanisms like prevention, avoidance, and detection that can be used to enforce data security properties including confidentiality, integrity, availability, authentication, and non-repudiation.