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What Is a Computer Worm (Worm Virus)?

In this cloud era, modern technology and computing have advanced in leaps and bounces. But such advancement has been accompanied by numerous cyber threats, and one such threat is computer worms. 

It is a severe malware program that replicates itself and spreads its copies in the computer and other computers connected to the network while staying active on the main hub. Having a computer worm in your system isn’t a good idea, as it will not only jeopardize every device in your network but also have serious implications. 

After reading this, you must be thinking, what is a computer worm? How does it work? What are the types? How to remove worms? What best practices can you follow to prevent them? Well, you shouldn’t be worried because it is exactly what we are going to discuss in this article.

So, let’s dive right into this article!

What is a Computer Worm (Worm Virus)?

A computer worm can be defined as a type of malware that has the capability to automatically propagate or make a copy itself and spread from one device to another. It is malicious software that self-replicates itself without requiring human intervention, making it one of the most impactful malware. It is like an infection that moves from computer to computer through a network to exploit vulnerabilities in a system or operating system

A computer worm typically uses an infected organization’s LAN network to spread itself to different devices connected to it. This type of malware keeps spreading more and more while remaining active in the primary infected system. .

Most of the time, these computers stay invisible to the user, and it becomes visible when the replication process consumes a lot of system resources, resulting in slowing of the computer. Besides computing resources, networks also get congested due to the propagation of worms. 

In addition, it enables attackers to steal sensitive information and bring a system to a halt. Wannacry is a well-known computer worm that can spread itself by taking advantage of vulnerabilities in Windows SMB servers. 

How Does a Computer Worm Work?

How Does a Computer Worm Work?

A computer worm operates by targeting vulnerabilities in an operating system or network protocols to install themselves and replicate them consecutively. Besides, they also gain entry into the system through loopholes in software, flash drives, or vulnerabilities in an application. 

Sometimes, an attack also introduces computer worms in your system through email attachments or spam emails. When you accidentally open the file or click on the link, the worm gets automatically downloaded, or you are redirected to a malicious website. 

Once the computer worm places itself in the system, it starts running on the newly infected and follows its directive while sneakily consuming the resources of the host. It stays active on the infected system for a long time until it is removed, and in that time, it starts spreading itself to as many vulnerable systems as possible. 

While the worm propagates to systems across the network, the attacker can leverage it to perform a range of attacks:

  • Stealing sensitive data.

  • Deleting files.

  • Overloading the network.

  • Drop other severe malware.

  • Create a backdoor.

  • Deplete hard drives.

Most Common Ways a Worm Spreads

Most Common Ways a Worm Spreads

Computer worms spread themselves by replicating themselves and don’t require any intervention. Worms sneakily spread on the infected system without being able to identify its existence. 

Usually, they spread on the infected depending upon the motive, but usually, the primary motive is to replicate itself again and again. Here are some common ways a worm spreads:

Unaddressed Vulnerabilities

Most of the time computer worms spread itself across the network by utilizing the unpatched vulnerabilities in the operating system or application. It targets the vulnerabilities and based on its motive, it starts showing its actions.

Shared Access

In many cases, systems or devices in an organization have shared access to drives and other components in a network, and this paves the path for worms to exploit it. These worms use the shared access to propagate itself to other devices.

File Sharing

P2P file networks often give the computer network the ability to spread to every device without getting interfered with.

Insecure Protocol

Insecure protocols serve as one of the most common mediums for computer worms to spread. Protocols like Telnet and TFTP often use default credentials or don’t require credentials so worm can utilize them for transporting them to the target system.


Another common way utilized by malicious actors to spread computer worms is utilizing phishing techniques. Attackers create fraud emails with malicious links and masquerade them with authentic look to compel users to download the attack or visit the website having worms. The attackers often utilize spear phishing where they target specific devices for ransomware attacks.

Instant Messengers

Nowadays, attackers often utilize instant messengers like IM platforms or text message platforms to spread computer worms. It helps in infecting devices on a large scale with different motives.

Removable Media

Removable media like USB flash drives or external hard drives serves as a common medium for computer worms to get transported to its targeted system. The worm can create a copy of itself in a removable media connected to the infected system and then spread itself to the new device where the removable media gets connected.

Why are Worms Dangerous?

A computer worm is one of the most impactful malware programs that affects a system or devices in a network in many ways. Attackers utilize worms to launch varied types of attacks like ransomware, DDoS, self-replication, providing backdoor entry, or installing malicious software. 

Even with top security solutions like antivirus, computer worms are extremely difficult to fully eradicate from a network of computers. They feed on the resources of the host device and stay hidden by masquerading as a traditional thing. Since they spread quickly and stay hidden in the system, it becomes a daunting task to fully recover the devices from the worm outbreak. 

For instance, when a worm outbreak takes place in an organization’s network or data storage environment, the security team has to utilize a lot of tools and time to eradicate it completely. There are some instances when a worm is directed toward a system without any malicious payload, but it still causes a serious threat, and the team has to spend time on incident response.

Types of Computer Worms

Types of Computer Worms

Usually, general users consider computer worms to be a single type of malware program. However, these worms are segregated into different types based on how they spread themselves across devices. Here are all types of computer worms that might affect your organization: 

Email Worms

Email worms serve as a popular computer worm type that spreads themselves by sending emails with malicious attachment. It is also known as a mass mailer worm, where the malicious program creates a copy of items as a self-executable attachment or link to the infected file. 

Attackers utilize phishing or social engineering techniques to make the email believable and compel users to click on the attachment.

File Sharing Worms

Another severe worm type is file-sharing worms, which create a copy of themselves on the shared folder and then propagate through the P2P network. 

Attackers usually disguise worms as media files, and users unknowingly download the file from the shared folder, leading to infection. Stuxnet and Phatbot are popular file-sharing worms that have infected numerous devices belonging to power utilities and water supply services.

IM Worms

IM worms are modern worm types that act as email worms, and they masquerade as attachments or links on social media platforms. Attackers design the link or attachment in such a way that the user unwittingly clicks on the link, thinking it is a legitimate attachment or link. 

Once the user falls victim, the worm gets installed, and it spreads through the instant message network. It utilizes the user’s contact to send a copy itself for spreading the malware program.


Cryptoworms are another worm type that encrypts all the data in the infected system, preventing users from accessing any of the files or operating systems. Malicious actors usually use this type of attack in ransomware, where they demand the user to pay ransom in crypto current in exchange for a decryption key.

IRC Worms

An IRC worm is a unique computer worm type that mainly targets IRC channels by spreading infected messages to chat rooms and message forums.

Internet Worms

Internet worms are another widely used worm type that exploits websites with poor security measures. Infecting the targeted site enables the attacker to attack the servers or organization managing it. In addition, it also infects the computer of users accessing the site by exploiting the vulnerabilities in the web browser.

Bot Worms

Another specialized worm type that is designed to infect systems or computers and turn them into a bot. Once the computers are infected, then attackers utilize botnets to perform DDoS attacks on the computers connected to the network. Conficker is a popular bot worm that infected thousands of systems in 2003.

Ethical Worms

Ethical worms are specialized worms used by security teams to spread them across networks and implement security patches for known vulnerabilities listed in the CVEs.

Computer Worm vs Virus

Computer worms and viruses might seem similar to many people as they both are malware and work by replicating themselves. Even though both the malware behave similarly, their replication methods differ from each other.

A computer virus depends upon human interaction for activation and requires a host to run it. Meaning that a virus will only infect your computer when the user installs the computer virus or somehow activates it. 

For example, a virus lying on the shared file system won’t infect your system unless it is activated. Usually, users are tricked into running malicious files so that the malware can spread across the network.

A computer worm, on the other hand, doesn’t require human interaction for activation or a host system. It can propagate from any system where the malware is downloaded or activated and from there by itself. Unlike viruses, computer worms are distributed to the system in different ways.

Examples of Computer Worms

Examples of Computer Worms

Computer worms have been present on the internet for decades. The first worm was created in 1971 and was named Creeper. After its introduction, there have been many notable computer worm cases that have caused major disruptions to businesses and networks. Here are examples of such computer worms: 

Morris Worm

Created by Robert Morris in 1988, an MIT graduate, the Morris worm is considered to be the first computer worm introduced that was widely propagated on the internet. This worm targeted vulnerabilities in several UNIX programs, causing them to overload, and it crashed over 60,000 UNIX machines connected to the ARPANET at that time. 

Even though Morris didn’t create it with malicious intention, the worm caused heavy financial damage, and it resulted in the first felony conviction under the 1986 Computer Fraud and Abuse Act.

SQL Slammer

Another popular computer worm surfaced on the internet was SQL Slammer and it caused havoc on many devices and networks. In 2003, this worm crashed thousands of routers around the world, launched DoS attacks on different internet hosts and disrupted internet traffic. This worm was spreaded quickly to 75,000 victim devices and affected them within 10 minutes.


The ILOVEYOU worm is considered to be one of the most dangerous computer worms that was created in May, 2000 and it was propagated through emails as love letter attachment. The attachment came as a text file or script run in instant messaging chat sessions. 

Once the victim opened the attachment, the worm sent itself to all the targeted victim’s contacts in Microsoft Outlook. It is estimated that the worm affected more than 50 million PCs within ten days and caused around $15 billion in cost to eliminate them completely from the PC. The spread wrecked so much havoc that Ford Motor Company had to shut their email service for a brief period.


Released in 2004, Mydoom is one of the fastest spreading computer worms in history that mainly targeted Windows computers. After it was released on the internet, it infected millions of systems operating in Windows OS that led to a probable damage of $38 billion at that time. Mydoom is still an active computer worm that accounts for 1% of the total email worm type present on the internet.


Stuxnet is a unique computer worm that came out around 2010 and was introduced via USB drives. According to security researchers this worm was created by Israel and US intelligence agencies in order to jeopardize the Iranian nuclear weapon production. 

Stuxnet exploited vulnerabilities in the Windows operating system of the nuclear labs which lead to malfunction of the nuclear centrifuges.

Storm Worm

Storm Worm made its entry on the internet in 2007, and it infected millions of systems through email. It baited millions of users by providing a subject line “230 dead as storm batters Europe” and to know about the cause users clicked on the link to know about Europe weather disaster.


WannaCry is a deadly ransomware attack that started in May 2017 and used computer worms to infect Windows systems by encrypting files on the user’s drive. It was a widespread attack that targeted millions of computers throughout the world. This worm also targets systems of large organizations that belong to banks, hospitals, logistics, and others. 

Through the worm, it was able to encrypt the files of the system, and then it contacted the owner to pay ransom in order to get keys to decrypt the files. It was estimated that the Lazarus Group from North Korea initiated the attack, and they brought massive financial loss.

Signs of a Worm Infection

Identifying computer worm infection in your system, network, or device can be a challenging task as it hides in plain sight. However, there are certain signs that can help you identify worms, and they are: 

  • Computer performance slows down over time with increasing CPU resource usage. You might also come across limited computing bandwidth without any context.

  • Some of the files and folders might be missing unexpectedly from the drive.

  • You will face unexpected crashing or freezing of your system without any explanation.

  • There will be atypical system behavior most of the time, where certain programs or websites might start and stop automatically.

  • You will find emails that are automatically sent to all your contacts without your approval.

  • While browsing drives, you will come across uncommon files or programs that you didn’t install on your device.

  • You might experience unusual messages, sounds, and often images on your device.

  • There will be unusual browser performance with a history of unusual sites.

  • You might also receive warning messages or reports from the antivirus program or the operating system.

How to Remove Computer Worms?

Removing computer worms from a computer, especially when it is connected across a network, can be a daunting task. Since worms spread quickly through the system, it is important to have a response plan in place. Response planning will enable the team to quickly identify worms in your system and minimize the impact.

To start an incident response, the security team needs to download all the required updates or tools in an external storage so that they can use them on the infected device. Then using signs or tools, they need to identify worms infecting the system. 

When the worm has been detected, you should make an effort to contain the attack by disconnecting the system from the network as well as the internet to prevent further propagation.

Once the worm is contained, you need to identify the system in which the worm has been affected and then update the antivirus to use it for scanning. The antivirus system will automatically uncover all the malware and worms in the systems across the network and clean the infected files. You can utilize various other scanning tools to identify and eliminate the worms.

Prevention Best Practices

Worms are one of the deadliest malware that can cause significant damage to a system, so it has become critical for everyone to take preventive measures to restrict them. Here are some best practices you can follow to prevent them: 

Leveraging Endpoint Protection 

Utilizing an endpoint protection like endpoint detection and response solution can help you proactively eliminate worms before they can make an impact. This solution can quickly identify infections and remediate them.

Utilizing Email Security

Worms are widely spread by attackers through email attachments so having email security can help you stop getting such emails. Email security solutions scans all the incoming emails for malicious attachments or links and blocks them before they reach you.

Using DNS Filtering

You can also utilize DNS filtering that will help you to filter out unwanted and malicious contents in your mail and prevent you from unwittingly clicking on malicious links or attachments.

Firewall Rules

Worms often gain entry into a network of an organization by exploiting unused protocols or any inbound connection. However, utilizing firewall rules can help you to filter and block all malicious traffic.

Protocol Security

It has been documented that worms often utilize insecure protocols like TFTP and Telnet to gain entry into a system. However, protocol security can help you disable all the insecure protocols and change default credentials to prevent remote access.

Utilizing Patch Management

Using patch management can help your organization to keep computer worms at bay. The patch management should take proactive measures and provide you visibility to high priority  worms that require quick patching.

Avoid Using Old Password

When it comes to passwords, you should always utilize a strong password, especially for router configuration, because it will keep you warm from exploiting default passwords. You should avoid using default credentials during network configurations.

Avoid Using P2P Programs

Whenever you are downloading any file from P2P or any other file sharing program, you can’t be completely sure the file is free from worms. When you are downloading any media file especially from a free site, you need to make sure you are downloading it from a trusted source.

How CloudDefense.AI Can Help?

After launching a computer worm, attackers always try to exploit the vulnerabilities of the target system or infect an endpoint device to spread the worm from there to others. When a worm enters the system, it starts spreading rapidly to other devices or systems in the network as they can self-replicate each other. 

It becomes a severe issue for the security posture. To help you prevent such disasters, CloudDefense.AI offers you a suite of practical solutions. To protect your system from computer worm attacks, you can utilize threat detection, data protection AI-SPM, and ransomware solutions. It not only offers you comprehensive protection against computer worms but also against other types of malwares. These solutions come equipped with advanced security features that accurately identify worms and provide protection against data encryption or modification. To learn more about the solutions, you can sign up for a free live demo.

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Anshu Bansal
Anshu Bansal
Anshu Bansal, a Silicon Valley entrepreneur and venture capitalist, currently co-founds CloudDefense.AI, a cybersecurity solution with a mission to secure your business by rapidly identifying and removing critical risks in Applications and Infrastructure as Code. With a background in Amazon, Microsoft, and VMWare, they contributed to various software and security roles.
Protect your Applications & Cloud Infrastructure from attackers by leveraging CloudDefense.AI ACS patented technology.

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