This document discusses types of attacks on computer and network security. It defines passive and active attacks. Passive attacks monitor systems without interaction and include interception and traffic analysis attacks. Interception involves unauthorized access to messages. Traffic analysis examines communication patterns. Active attacks make unauthorized changes and include masquerade, interruption, fabrication, session replay, modification, and denial of service attacks. Masquerade involves assuming another user's identity. Interruption obstructs communication. Fabrication inserts fake messages. Session replay steals login information. Modification alters packet addresses or data. Denial of service deprives access by overwhelming the target.