This document discusses different types of malware such as viruses, worms, Trojans, and blended threats. It describes how viruses spread by infecting files and requiring user interaction, while worms can spread automatically from computer to computer by exploiting vulnerabilities. Trojans appear useful but have hidden malicious functions. Blended threats combine characteristics of different malware types. The document also outlines how malware infects systems, hides, and can be detected through techniques like signatures and behavior analysis.