Virus vs Worm
The primary difference between a virus and a worm is that viruses must be triggered by the activation of their host; whereas worms are stand-alone malicious programs that can self-replicate and propagate independently as soon as they have breached the system. Worms do not require activation—or any human intervention—to execute or spread their code.
Viruses are often attached or concealed in shared or downloaded files, both executable files—a program that runs script—and non-executable files such as a Word document or an image file. When the host file is accepted or loaded by a target system, the virus remains dormant until the infected host file is activated. Only after the host file is activated, can the virus run, executing malicious code and replicating to infect other files on your system.
In contrast, worms don’t require the activation of their host file. Once a worm has entered your system, usually via a network connection or as a downloaded file, it can then run, self-replicate and propagate without a triggering event. A worm makes multiple copies of itself which then spread across the network or through an internet connection. These copies will infect any inadequately protected computers and servers that connect—via the network or internet—to the originally infected device. Because each subsequent copy of a worm repeats this process of self-replication, execution and propagation, worm-based infections spread rapidly across computer networks and the internet at large.
How Do Computer Viruses and Worms Spread?
Viruses and worms are a subcategory of malicious programs, aka malware. Any program in this subcategory malware can also have additional Trojan functions.
Viruses
Viruses can be classified according to the method that they use to infect a computer
- File viruses
- Boot sector viruses
- Macro viruses
- Script viruses
Worms
Worms often exploit network configuration errors or security loopholes in the operating system (OS) or applications
Many worms use multiple methods to spread across networks, including the following:
- Email: Carried inside files sent as email attachments
- Internet: Via links to infected websites; generally hidden in the website’s HTML, so the infection is triggered when the page loads
- Downloads & FTP Servers: May initially start in downloaded files or individual FTP files, but if not detected, can spread to the server and thus all outbound FTP transmissions
- Instant Messages (IM): Transmitted through mobile and desktop messaging apps, generally as external links, including native SMS apps, WhatsApp, Facebook messenger, or any other type of ICQ or IRC message
- P2P/Filesharing: Spread via P2P file sharing networks, as well as any other shared drive or files, such as a USB stick or network server
- Networks: Often hidden in network packets; though they can spread and self-propagate through shared access to any device, drive or file across the network
How to Protect All Your Devices from Viruses and Worms
Viruses, worms and malware most often exploit security vulnerabilities and bugs. For this reason, it is crucial to keep current with all OS and application updates and patches. Unfortunately, keeping current with updates and being vigilant simply are enough. There are many exploits and vectors that can get viruses and worms into a network or onto a computer or mobile device.
These days, comprehensive cyber security is mandatory for all your devices—desktops, laptops, tablets and smartphones. To be effective, cyber security solutions must provide real-time protection for all your activities, from emails to internet browsing, not just periodic hard drive scans. Furthermore, today’s best security software products are not static one-time installations with periodic updates. A quality cyber security product is provided as a service, known as SaaS (Software-as-a-Service). This means that in addition to monitoring your devices in real-time, the software itself is updated in real-time with the most current information about existing and emerging threats, how to prevent them and how to repair their damage.
Source: https://www.kaspersky.com/resource-center/threats/computer-viruses-vs-worms