This module covers Trojans and backdoors. It begins with an introduction to Trojans, describing them as small programs that run hidden on infected computers and allow attackers access. It then discusses overt and covert channels, the different types of Trojans including remote access and data-sending Trojans, and how Trojans can get into systems. The document provides indications of Trojan attacks, popular Trojans found in the wild like Tini and NetBus, and tools used to send Trojans like wrappers and packaging tools. It also discusses techniques like ICMP tunneling, HTTP Trojans, and reverse connecting Trojans. Finally, it discusses tools for detecting and preventing Trojan infections.