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

The main difference between a virus and a worm lies in their methods of propagation. A virus requires user action to activate, such as opening a file or executing a program that contains the virus code. In contrast, a worm is capable of self-replicating and spreading across networks without any user intervention, which allows it to propagate rapidly. This fundamental distinction underlines the behavior of these two types of malware, where user interaction is essential for a virus to work while a worm operates autonomously.

The other options do not accurately capture the essential differences between a virus and a worm. For instance, viruses are not inherently classified as network attacks; they can spread through various means such as removable media or email attachments. Additionally, saying a worm executes faster than a virus is misleading because execution speed can vary based on numerous factors. Lastly, a worm does not require a host program to function—the worm itself is a standalone program, whereas a virus attaches itself to a host file to launch its attack.