What is the primary difference between a virus and a worm?

The primary difference between a virus and a worm is that viruses require human interaction for activation while worms can replicate and spread independently without any user intervention. A virus attaches itself to a host file or program and is executed when that file or program is run by a user. In contrast, a worm is designed to automatically exploit vulnerabilities in networked systems to propagate itself from one computer to another, often using mechanisms like email or network connections. This characteristic of worms allows them to spread rapidly across networks, whereas viruses rely on user actions to spread and infect other systems.

The other options do not accurately distinguish the fundamental differences between these two types of malware. For instance, the idea that viruses must be activated before a worm can replicate misrepresents the nature of how they operate, as worms do not need a virus to function. Additionally, not all viruses are limited to Windows operating systems; they can affect various platforms, and worms are not specialized denial-of-service attacks but instead focus on self-replication and spreading. Lastly, while both viruses and worms fall under the broader category of malware, they are defined by their unique methods of propagation and behavior.