What’s the Difference between a Virus and a Worm?

A man tapping a computer screen to identify a malware worm.

With the rise in cyberattacks and cybercriminal behavior across the US since the pandemic it’s now more important than ever to maintain a high level of digital security on both your personal and professional devices. However, understanding what kind of security you need depends on the kinds of threats that you (or your family) are likely to encounter.

Unfortunately, it is often difficult for users to learn about the important aspects of cybersecurity because of all of the jargon; from spyware, malware, and adware to viruses, man-in-the-middle attacks, and cross-site scripting, all of these terms have specific meanings that can be quite overwhelming at first. That’s why we decided to create this guide, explaining simply and clearly the three main cyber threat terms that you’re likely to come across: “Viruses”, “Worms”, and “Malware”.

This can be a little confusing at first, as both a virus and a worm (sometimes referred to as a malware worm) are malicious pieces of code that “replicate” in a victim’s computer system (much like a virus in a human body’s system). The primary difference between a virus and a worm is that viruses must be triggered by their host/victim’s interaction with the infected file. In contrast, worms are stand-alone malicious programs that can self-replicate and propagate independently as soon as they have breached the system. In short, worms do not require activation (or any human intervention) to execute or spread their code around your system.

When entering your computer, viruses are often attached or concealed in shared or downloaded files, both executable files, a program that runs a script, and non-executable files, such as a Word document or an image file. When the host file is accepted by the victim’s system, the virus remains dormant until the infected host file is activated. Only after the host file is activated can the virus run, executing its malicious code and replicating it to infect other files on your system. In general, viruses are often designed to destroy personal files or seize control of someone’s digital devices.

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 (of any kind), it can then run, self-replicate, and propagate without a triggering event (like opening the infected file). 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 when deployed.

What is the Difference between Malware and a Virus?

The difference between malware and a virus is that malware is the official term used to describe any piece of malicious code (like a worm or a virus) that is designed to infect and cause harm to another person’s computer system, regardless of how it attacks the victim’s files or how it infiltrates the system. This can be a little confusing at first, as most people (not in the cybersecurity industry) use the term “virus” when something has infected their computer when actually they mean that some malware has found its way into their system and infected it.

As mentioned above, a virus is a type of malware that can infect a victim’s system and is triggered by the victim themselves when they try to access the infected file sent by the hacker.

A computer showing a virus has been detected and is spreading.

How Do Computer Viruses and Computer Worms Spread?

Viruses and worms are a subcategory of malicious programs or malware. Any program in this subcategory can also have additional Trojan functionalities.

Viruses: Viruses can be classified according to the method that they use to infect a computer and spread from one user to another (in fact, they spread in similar ways to worms):

File viruses: They are attached to files in emails, direct messages, or downloads, and can be shared to the victim’s computer much like a normal file shared amongst internet users online.
Boot sector viruses: These viruses are often spread using physical pieces of hardware. For example, an infected USB drive connected to a computer will transfer the virus when the drive’s Volume Boot Record (VBR) is read, then modify or replace the existing boot code with the infected code.
Macro viruses: As they are written in the same macro language used to create software programs (like Excel or Word), they usually attack software (as opposed to the whole system) as an attachment to a file via emails (generally, they are found hiding in phishing scam emails).
Script viruses: These tend to be less common as they are generally spread through clicking webpage ads. After you’ve clicked, the virus tries to breach your browser’s security vulnerabilities. The effects of this virus range from stealing cookies to shutting down your system at will.

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, these worms are the most common.
Internet: Via links to infected websites; generally hidden in the website’s HTML, so the infection is triggered when the page loads on your browser.
External Drives: It’s possible to hide a computer worm in a USB stick or an external drive so that it infects the victim’s system when the hardware is connected.
Downloads & FTP Servers: These worms may initially start in downloaded files or individual FTP files, but if not detected, can spread to the server and, thus, through all outbound FTP transmissions.
Instant Messages (IM): Transmitted through mobile and desktop messaging apps, generally as external links, including on native SMS apps, WhatsApp, Facebook Messenger, or any other type of ICQ or IRC message system.
P2P/File sharing: 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 be spread and self-propagate through shared access to any device, drive or file across the associated network.
Software Holes: As noted above, worms have been known to enter systems via old software without modern security patches.

How to Protect All Your Devices from Viruses, Worms, and Malware

Viruses, worms, and most forms of malware often exploit security vulnerabilities and bugs, causing a number of complications for the user, including slower functionality, a constantly running hard drive, corrupted files, and unwanted ad pop-ups (even when offline). For this reason, it is crucial to keep up to date with all OS and application updates and patches. Unfortunately, keeping current with updates and being vigilant simply isn’t 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.

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