What Is the Main Difference Between a Worm and a Virus?

Bojan Jovanovic

Updated: July 14, 2023

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Having antimalware software and a firewall to protect our devices from every type of malware is essential. Still, one of the most common ways people fail to protect themselves is by never updating their operating system (OS), thus leaving it vulnerable to attacks. It’s one of the essential steps that often gets overlooked even by major companies. 

Figuring Out Malware: Virus vs. Worm

The main difference between a worm and a virus is how they self-replicate. As soon as it breaches the system, a worm will spread through the network independently and infect devices on its path without users realizing what is happening. In contrast, the user has to trigger the virus by interacting with it.

Worms and viruses also have some similarities. Both are extremely contagious and capable of copying themselves rapidly. When it comes to viruses and worms, it’s safe to say that you don’t want any of them infecting your system. 

Computer Worm vs. Virus

Because a virus needs to be run from an executable file, cybercriminals will usually employ phishing attacks to infect their targets. Work emails titled “Please review” are common in the office, and all it takes is one employee to fall for a fake email like that. 

The email will have an attachment that holds the virus. Nothing will happen until the user triggers the virus by opening the file, and once triggered, it will start to spread and self-replicate throughout the system. A computer virus can also use a newly infected host to send out emails with copies of itself.

As mentioned before, the difference between a virus and a worm is how they self-replicate throughout the computer network.

The worm doesn’t require a user to activate it, as it exploits system vulnerabilities to infect machines through the network as soon as it breaches the network for the first time. It can also be deployed from a file downloaded to the user’s machine while visiting an infected website. Once it infects the PC, the worm will scan the network and start spreading to all the devices on the network. 

What often happens in a worm-based infection is that a worm will install backdoors on all the machines it gets in contact with. Then, the cybercriminal will use them to launch an attack.   

Something similar happened with the WannaCry ransomware attack in 2017. Namely, the attacker used a vulnerability in Microsoft’s sharing protocol to install backdoors before launching a ransomware attack. 

Types of Viruses and Worms

Viruses and worms can be further divided into types according to the method used to infect a device.

Viruses

1. File viruses

This is the most common type of virus. It’s located in an executable file where it lies dormant until the user ​​triggers the virus. 

2. Boot sector viruses 

The virus is distributed via external file storing units. Once attached to the PC, it will automatically load into the memory, giving it complete control over your PC the next time you boot it up.  

3. Macro viruses 

The most common office virus spreads via email with a Microsoft Office attachment. When the file is open, it will ask for a macro to be installed. The macro is the computer virus.

4. Web scripting viruses

The attacker uses a website vulnerability to insert malicious links into the HTML code and then install malicious software on devices that visit the websites. The virus can steal your cookie data and use it to impersonate you. It’s the most common way people lose their accounts on social media. 

Worms

1. Email

Email worm malware works in a way that’s similar to an email-transmitted virus. It can also have an attachment or a shortened URL that leads to a website that will infect the PC. Unlike a virus, the worm-containing attachment doesn’t have to be run, only downloaded. Once activated, the worm-based infection will spread throughout the network.  

2. Internet

The attackers can use popular websites’ vulnerabilities to distribute malicious software to the PCs from which the websites have been accessed. This will further spread the worms throughout the local network. 

3. Instant Messaging

An instant messaging worm works in a similar way to an email worm, although it uses a different method of distribution. It can use any popular messaging app or even an SMS to send out infected files or links to all of your contacts. 

4. File-sharing

Sharing files over a P2P network can be a source of worm malware infestation. Although the downloaded file may look real, it could be infected with a worm software that will continue spreading across the network. 

5. Networks

Once the PC is infected, the worm will scan the network, and it will continue to spread to any device across the network hidden as a network packet. This can also happen over an internet connection, but luckily, such attacks are easy to spot by firewall protection as long as it’s kept up to date. 

How To Protect Yourself from Viruses and Worms 

Computer viruses are more common and easier to detect than worms, but that doesn’t mean that worms are unstoppable. Here are some basic actions that will help you protect yourself: 

• Install good antimalware software and a firewall
• Keep your system and antimalware software up to date
• Double-check the sender of the email before downloading and running anything
• Do not click on any unverified links 
• Do not visit unverified websites

Because worms most commonly exploit a security vulnerability, keeping your system updated is paramount. Occasionally, cybercriminals reverse engineer a security update to see what is patched and launch an attack aiming at those machines that haven’t installed the latest security fix.