The situation described involves an insider using a packet crafting tool that generated malformed TCP/IP packets, resulting in the crash of the main server's operating system and restricting employee access. This scenario is indicative of a Denial of Service (DoS) attack. A DoS attack aims to make a machine or network resource unavailable to its intended users by temporarily or indefinitely disrupting services of a host connected to the Internet. Malformed packets can cause systems to crash, thereby denying service to legitimate users.