Exploring the Differences: Worms vs. Viruses

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Maxym Chekalov
Written by
Maxym Chekalov

Updated · Nov 16, 2023

Maxym Chekalov
SEO Specialist | Joined June 2023 | LinkedIn
Maxym Chekalov

With a master's degree in telecommunications and over 15 years of working experience in telecommunic... | See full bio

Florence Desiata
Edited by
Florence Desiata


Florence Desiata
Joined June 2023 | LinkedIn
Florence Desiata

Florence is a dedicated wordsmith on a mission to make technology-related topics easy-to-understand.... | See full bio

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Worms and viruses are both known cybersecurity threats that are often misconstrued for one another. However, these two are entirely different. 

A worm is a type of malware with the primary purpose of self-replicating. Its infection rate made it the world’s 4th most common malware—with 6.23% detections.

In comparison, viruses are malware that spreads by attaching to other files. It is also one of the most common types of malware, with a detection rate of 13.02%

Learn more about these two types of malware and what makes them different from each out. Find out what else they can do and how to protect your devices against them.

🔑 Key Takeaways

  • Being notorious cyber threats, worms and viruses are distinct types of malware that are often confused with each other. 
  • Worms self-replicate and spread via networks, while viruses attach to files and need user interaction to spread.
  • Notable worm and virus attacks include Mydoom, Nimda, Code Red, and Klez. All showcased diverse infection methods and potential damage.
  • Protect devices by downloading only from trusted sources, using strong passwords, regular updates, and installing antivirus tools.

Worms and Viruses: What are the Differences?

Worms and viruses cause damage to a user’s device. Other than that, they have noticeable differences.

Check out the table below to see the key differences between a worm and a virus:





Spread independently

Need a host file to spread

Mode of Spreading

Through networks and vulnerabilities

Through infected files and attachments



Attach to files and require user actions to spread


Can infect devices automatically

Require user action to execute and spread

Impact on Systems

Consume resources; 

Cause crashes and network failures

Slow down systems;  modify, delete, and steal data

To get a better grasp of what makes them different, it is vital to understand what worms and viruses are as well as how both of these malware work. Read on. 


📖 Definition

Worms are malware that can self-replicate and travel from the device using a computer network. They usually infect vulnerable machines and spread themselves to multiple devices.

Due to their nature, worms can easily avoid suspicion as they stay with the computer’s memory. An infected device thinks the worm is part of its system.

Worms consume resources like memory, CPU, and network bandwidths. It also causes system crashes and network failures. 

Unlike most malware, worms can stand alone. They don’t need host files to spread. To spread, they find and exploit vulnerabilities in a computer system. 

Take a look at the video below to see what Kaspersky has to say about what worms are and how they spread. 

Types of Worms

This malware is more common than you think. Some of the worms that you should be aware of are:

File Sharing Worms

Found in shared files like movies, music, files, etc.

Email Worms 

Contains files that can install the worm on the computer.

Network or Internet Worms

Spread from a Local Area Network through the Internet and enter connected devices

Instant Messaging Worms

Send clickbait messages to a user’s contacts to install themselves on their devices

Effects of Worms on Your Computer

Since your device may think of a worm as part of its system, the malware can cause serious damage—-all without being detected. 

These are some of the things that a worm can do to your device: 

Frequent freezing and crashing of your computer

Frequent freezing and crashing of your computer

Automatic opening and running of programs

Automatic opening and running of programs

Modified and missing files

Modified and missing files

Spam emails are sent to your contacts

Spam emails are sent to your contacts

Overloaded web servers

Overloaded web servers


Cisco defines viruses as: 


[...} a type of malware that self-replicates by inserting its code into other software programs. It spreads from one computer to another, leaving a path of destruction as it propagates.”  

This malware can slow computer systems by filling up disk spaces and affect hard disk drives by formatting them.

A computer virus infection can happen through network sharing. However, it commonly occurs in file sharing using hard drives, flash drives, and email attachments.

Unlike worms, a virus relies on a user and a host to spread. It attaches itself to an executable file (.exe). The virus starts spreading once the file is transferred to another device and launched.  

The video below sums up how viruses work and how they spread. Check it out. 

Types of Viruses

Around 90% of desktop and laptop users use antivirus software. This number continues to grow as more and more cyberattacks are reported. 

However, the more cautious people are getting, the more online threats like viruses also evolve. New and stronger viruses are launched continuously. 

All the viruses are classified under these categories: 

Macro viruses

Spread through shared network drives or email attachments

Resident viruses

Can infect files and networks even if the infected source file is removed

File infectors

Attached files from infected devices that  activate and spread when opened

Polymorphic viruses

Most difficult to detect since they change codes when infecting a new system

Multipartite viruses

Also challenging to remove because they can infect both boot sectors and files

Effects of Viruses on Your PC

Viruses are considered a big threat to online security since most people know and even experience their effects. 

Here are what most viruses can do to your computers: 

Computer functions are slower than usual

Computer functions are slower than usual

Missing  due to data modification and deletions

Missing  due to data modification and deletions

Weird behavior on the computer functions

Weird behavior on the computer functions

Programs failing when opened or used

Programs failing when opened or used

Ads and pop-ups start to increase

Ads and pop-ups start to increase

Biggest Worms and Virus Attacks Worldwide

Due to their devastating effects, it’s no wonder worms and viruses are classified as major dangers to cybersecurity. 

However, these malware do not just affect an individual’s device. They can also target multiple devices at the same time. Some worms and viruses even attacked popular institutions and organizations. 

Discover four of the world’s most known worm and virus attacks below. 

1. Mydoom Worm 

Email with an infected attachment

Mydoom worm scraped information from vulnerable and infected machines. The worm then emailed several copies of its virus to infected devices.

The emails contained weird phrases and messages such as “I’m just doing my job, nothing personal, sorry.” 

People also reported that these emails have attachments that double occasionally.

Due to the self-replication of infected emails, statistics stated that this worm sent 25% of the world's total emails between 2004 and 2009.

💡Did You Know?

In 2004, the Mydoom Worm recorded a total damage of $38 billion. Another name for this worm is “Novarg.” 

2. Nimda

The Nimda virus became famous in September 2001 because it significantly damaged the digital world, subsequently spreading in any way possible.

During its peak, the Nimda virus caused 160,000 infections in digital companies like Della and Microsoft. It also marked millions of dollars worth of damage to systems.

🎉 Fun Fact

The name "Nimda" is "admin" spelled backward. This stands for the ability of the virus to exploit a computer’s administrative vulnerabilities.

3. Code Red Worm 

A front page infected by a Code Red Worm virus

The Code Red Worm malware was released on July 13, 2001. In less than a week, the worm garnered 359,000 victims.

Webpages infected with Code Red Worm displayed the words: “Hacked by Chinese.” Although other variants of worms leave traces, this worm left no files on the hard drives it infected.

4. Klez

Klez H variant showing a random attachment with a virus

2001 was an unlucky year for many computer devices and networks. The worm known as “Klez” wreaked havoc in 2001, resulting in $19.8 billion worth of damages.

This mass-mailer worm targeted Microsoft Windows. The Klez worm takes the form of an email, with the sender being an email address from an infected computer's address book. 

Klez evolved into different variants that got more and more destructive. These variants infected all sorts of files and devices. 

Fortunately, as technology developed, Klez and its variants eventually died. 

How To Protect Your Devices From Worms and Viruses?

While malware and viruses can be detected by tools or casual monitoring, it is still best to reduce the risk of malware infection to zero. 

You can do that by keeping your devices protected using the techniques below: 

1. Always Download Software From Legitimate Sources

Before downloading and installing software, make sure to get them from legit websites.  Fake or sketchy websites may contain scams and links to malware.

Here are some tips on how to spot the legitimate ones:

The website URL should be “HTTPS” and not “HTTP.”

The website URL should be “HTTPS” and not “HTTP.”

Look for the“lock” icon on the web browser’s window.

Look for the“lock” icon on the web browser’s window. 

Double-check the spelling and grammar of the website. 

Double-check the spelling and grammar of the website. 

Search for the website’s privacy policy. 

Search for the website’s privacy policy. 

Look if they have a social media presence.

Look if they have a social media presence.

2. Use Unique and Strong Passwords

Passwords are links to your personal data and information. Having weak passwords can lead to hacking or malware attacks. 

The best way to avoid hacking and potential attacks, avoid using common password ideas such as phrases, birthdays, and known media characters.

A good and strong password needs to have 8 characters, special characters, or a combination of letters and numbers.

👍 Helpful Article

Discover effective ways to create better passwords by knowing the do’s and don’ts when making your passwords for a safer browsing experience.

3. Practice the “Think Before You Click” Method

Malware attacks always start with one click. When done, they spread quickly, causing irreparable damage. 

Practice this by always checking the data, website, platform, and applications you access to know if it's a potential virus or worm. 

Additionally, click a safe and protected file and remember to view and download files only from trusted sources. 

💡Did You Know?

Passwords are not limited to sets of randomly generated letters and numbers. Modern technology now features passwordless authentication via OTP, biometrics, and more. 

4. Update Your Computer Regularly

Regular updates from your browser, system, and applications are beneficial. These updates contain necessary information and features that remove flaws in any software.

5. Install an Antivirus Tool

Antivirus applications are tools that protect your computer from viruses. A simple antivirus scan can prevent malicious activities from executing, avoiding potential infections.

To access antivirus applications, follow these steps:

Note: The steps below used McAfee antivirus. This antivirus tool offers a 30-day trial that lets you experience top-tier malware detection and protection for free. 

Step 1: Look for an antivirus tool that works best for you. 

McAfee website

Step 2: If you already have an account, sign in. If not, click “Create one now” and set up a McAfee account. 

McAfee’s account creation page 

Step 3: Download and install the app. 

Step 4: Modify its features according to your preferences. 

McAfee’s security features 

After your 30-day trial, you might want to consider signing up for a subscription. For as low as $150 annually, you can get 24/7 protection from malware. 

This Premium plan also comes with a VPN and a password manager. It even offers scans to help clean up your personal data and accounts on the web. 

Final Thoughts

Learning and differentiating one malware from another plays a significant role in protecting devices. Through this, users can find solutions quickly 

Consequently, by knowing how they spread or replicate, users can prevent malware attacks from happening, leading to less damage to systems, files, and devices.

Like any other malware, user intervention and awareness are still needed to prevent these from resurfacing.


Can a worm be a virus?

No. They can both damage your computer, but they are two different types of malware. Worms can spread through a computer network, but a virus can’t.

What are the similarities between worms and viruses?

Aside from being both types of malware, worms and viruses can spread rapidly. They can also cause severe damage to a device if they’re not removed. 

Are all viruses Trojan?

No. Trojans are not viruses, as they are classified as malware. Viruses attach themselves to files as codes to spread and infect. Meanwhile, Trojans pretend to be genuine software or files to trick users into downloading and clicking them. 


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