Common Types of Computer Worm and How to Avoid Them

Table of Contents

Computer worms are self-replicating malicious programs that spread through computer networks. Common types include email worms, network worms, and file-sharing worms. To avoid them, keep your operating system and software up to date, use strong and unique passwords, be cautious when opening email attachments or clicking on suspicious links, use reliable antivirus software, and regularly back up your data.

What are the different types of Computer worms?

Computer worms are malicious software programs that have the ability to self-replicate and spread across computer networks without requiring user interaction. Unlike viruses, which attach themselves to host files or programs, worms are standalone entities that can independently exploit vulnerabilities in operating systems, network protocols, or applications to gain unauthorised access to computers. Once inside a system, worms can duplicate themselves and continue to spread to other connected devices, causing disruptions, stealing sensitive information, or performing other malicious activities.

Here are some common types of computer worms based on how they spread!

Email Worms:

Email worms are malicious programs that spread by leveraging email systems. Email worms spread primarily through email attachments or links. Worms use vulnerabilities in email clients or rely on social engineering techniques to trick users into opening infected attachments or clicking on malicious links. Once opened, the worm can replicate itself and send copies of itself to the victim’s email contacts.

Real-life Incident – ILOVEYOU Worm

ILOVEYOU, also known as Love Bug or Love Letter, was a worm that emerged in 2000 and spread through email as a malicious attachment with the subject line “ILOVEYOU.” When opened, the attachment unleashed the worm, which overwrote files, stole passwords, and sent copies of itself to all contact lists in the victim’s address book. It caused widespread damage, infecting millions of computers worldwide.

Network Worms:

Network worms are self-replicating programs that spread through computer networks. Network worms spread by exploiting vulnerabilities in network services, protocols, or operating systems. They typically target computers connected to the same network or through the internet. These worms can use various propagation techniques, such as exploiting software vulnerabilities, brute-forcing weak passwords, or using self-replicating mechanisms to infect other vulnerable systems.

Real-life Incident- The “Conficker” worm:

It emerged in 2008 and targeted Windows operating systems. Exploiting a vulnerability in Windows, it spread rapidly across networks, infecting millions of computers globally. While the Conficker worm had a widespread impact, it didn’t specifically target any particular big brands or organisations.

Uncover hidden worm activities within your network infrastructure with our NETWORK Vulnerabilities Scanner!

File-Sharing Worms:

File-sharing is a type of worm that propagates through file-sharing networks, peer-to-peer (P2P) networks, or shared drives. They often disguise themselves as legitimate files or software applications and spread when users download or share infected files. These worms take advantage of the interconnected nature of file-sharing networks to quickly spread across multiple systems. Once a user downloads and opens an infected file, the worm can replicate itself and spread to other shared locations or systems connected to the network.

Real-life Incident – Nimda Worm:

The “Nimda” worm in 2001 spread through various file-sharing networks and exploited multiple vulnerabilities to infect systems and compromise data.

Instant Messaging Worms:

Instant messaging worms spread through popular instant messaging platforms or chat applications. They misuse vulnerabilities in the messaging software or employ social engineering techniques to trick users into clicking on malicious links or downloading infected files sent through instant messages. Once a system is infected, the worm can automatically send messages containing its payload to the victim’s contacts, facilitating its further propagation.

Real-life Incident – Kelvir worm:

The “Kelvir” worm, observed in 2005, propagated through instant messaging platforms, including MSN Messenger, by sending malicious links to contacts.

USB Worms:

USB worms spread through removable storage devices, such as USB flash drives. When an infected USB drive is connected to a computer, the worm can automatically execute and copy itself onto the host system. USB worms often take advantage of the autorun feature in operating systems, allowing them to execute automatically whenever the infected USB drive is connected to another computer, thus spreading the infection.

Real-life Incident – Stuxnet worm: 

The “Stuxnet” worm, discovered in 2010, targeted industrial control systems and was spread through infected USB drives, exploiting vulnerabilities to compromise systems.

Additional Real-Life Computer Worm Examples

The examples below are just a few of the common computer worms that have caused significant disruptions in the past. It’s worth noting that the threat landscape is constantly evolving, and new types of worms can emerge over time.

  1. Blaster Worm: The Blaster Worm, also known as Lovsan or MSBlast, emerged in 2003 and targeted Microsoft Windows operating systems. It exploited a vulnerability known as the DCOM RPC vulnerability to spread and launch distributed denial-of-service (DDoS) attacks.
  2. Nimda Worm: Nimda was a complex worm that emerged in 2001 and spread through multiple methods, including email, network shares, and web servers. It misused various vulnerabilities in Microsoft Windows and web servers like IIS. Nimda had the ability to infect both web servers and client systems.
  3. SQL Slammer Worm: Slammer, also known as SQL Slammer, was a fast-spreading worm that appeared in 2003. It exploited a vulnerability in SQL Server and MSDE (Microsoft SQL Server Desktop Engine) to propagate itself rapidly. The slammer caused widespread network congestion and disrupted various internet services.
  4. Morris Worm: The Morris worm, created in 1988, was the first computer worm designed to self-replicate and spread across interconnected computers, utilising multiple methods of propagation. This caused widespread disruption, infecting thousands of computers and significantly slowing down affected systems. Its unintended side effects, such as exploiting vulnerabilities multiple times and causing system crashes due to excessive replication, led to increased awareness of the need for robust cybersecurity measures and the development of incident response protocols.

It is crucial to keep your operating system and software up to date with security patches and use reliable antivirus/anti-malware software to protect against such threats. Managed Security Services: Learn More!

Also Read: Most Common Types of Spyware and how to avoid them

How does a Computer worm spread?

A computer worm is a type of malware that is designed to self-replicate and spread across networks or systems. Unlike computer viruses, which require the execution of infected files, worms can propagate independently. Here’s how a computer worm spreads:

  • Initial Infection: A computer worm typically enters a system through various means, such as exploiting software vulnerabilities, using social engineering techniques, or disguising itself as a legitimate file or program.
  • Replication: Once inside a system, the worm begins to replicate itself. It creates copies of its own code and may modify its behaviour to avoid detection by antivirus software.
  • Exploiting Network Connections: A successful computer worm can now search for other vulnerable computers connected to the same network or across the internet. It scans IP addresses, open ports, or other network connections to find potential targets.
  • Infecting Other Computers: When the worm discovers a vulnerable computer, it attempts to use security weaknesses, such as unpatched software or weak passwords, to gain unauthorised access. Once inside, it proceeds to infect the newly compromised system.
  • Spreading Across the Network: The worm continues to replicate and spread from one compromised system to another, creating a chain of infected computers. This rapid propagation allows the worm to reach many computers within a short period.
  • Network Propagation: A worm usually takes advantage of network connections and protocols to move from one system to another. It can exploit vulnerabilities in network services or use default credentials to gain access to network devices, such as routers or servers, to further its reach.
  • Email Worms and Social Engineering: In the case of an email worm, it may use social engineering techniques to trick users into opening infected email attachments or clicking on malicious links. Once opened, the worm can use the victim’s email contacts to send copies of itself, initiating a new cycle of infection.
  • Worm Outbreak: If a worm manages to infect a significant number of computers, it can lead to a worm outbreak, where the rapid spread overwhelms networks and causes widespread disruption.

The propagation methods and behaviour of computer worms can vary, and their impact can be mitigated through security measures such as regular software updates, strong passwords, network segmentation, and the use of S360 for business.

What are the differences between a virus and a worm?

A Virus is a type of malware that infects a computer by attaching itself to a host file or program and requires the execution of the infected file to spread and cause harm. It relies on user actions or the execution of infected files to propagate.

A Worm is a type of malware that is a standalone computer program capable of self-replication and spreading across networks or systems. It can exploit vulnerabilities, use various propagation methods, or create copies of itself to infect other systems without needing a host file.

Let’s look at some of the major differences below-

  • Spread Method: Viruses typically require user interaction or the execution of an infected program to spread, whereas worms can spread autonomously without user intervention.
  • Infection Approach: Viruses typically attach themselves to executable files or infect existing files, while worms are standalone computer programs that can replicate and spread independently.
  • Infected Computer: To infect a computer, a virus needs an infected file to be executed, while a worm can exploit vulnerabilities or use various propagation methods to infect a computer without relying on another file.
  • Replication: Viruses rely on the host file or program to replicate and spread, while worms can create copies of themselves and spread to multiple systems without needing a host file.
  • Scope: A virus tends to affect a limited number of systems and relies on user actions for propagation, while a worm can spread rapidly across networks, infecting many systems in a short time.
  • Payload: Both viruses and worms can carry malicious payloads, but worms might focus more on self-replication and spreading rather than causing direct damage to the infected system.
  • Internet Worm: A worm is a specific type of malware known as an internet worm, while a virus is a broader category of malware that includes various types.
  • Self-Sustainability: Worms are designed to operate independently and can continue spreading without user interaction or relying on specific conditions, while viruses require the presence of an infected file or program to continue spreading.

Also Read How Can You Avoid Downloading Malicious Codes?

How to prevent Computers from worm infection?

To prevent computers from worm infections, it is crucial to implement effective security measures. Here are some key practices:

  • Install Antivirus Software: Deploy reputable antivirus software on all computers and keep it up to date. Antivirus programs can detect and remove known worm viruses, providing a layer of defence against infection.
  • Regular Software Updates: Keep operating systems, applications, and security patches up to date. Worms often exploit vulnerabilities in software, so timely updates help to close those security loopholes.
  • Exercise Caution with Email and Downloads: Be cautious while opening email attachments or clicking on links, especially from unknown or suspicious sources. Worms may disguise themselves as harmless files or links, so exercise discretion and use email filtering to block malicious content.
  • Safe Browsing Practices: Avoid visiting malicious websites or clicking on suspicious ads. Worms can be distributed through drive-by downloads or malicious advertising, so ensure that web browsers and plugins are updated and use ad-blockers for added protection.
  • Network Security: Secure network infrastructure by using firewalls, intrusion prevention systems, and strong network segmentation. Limit unnecessary network services and close unused ports to reduce the attack surface for worms to exploit.
  • Regular Backups: Maintain regular backups of critical data and ensure they are stored separately from the main network. In case of infection, having up-to-date backups helps recover data and minimises the impact of a worm attack.
  • Incident Response and Removal: In the event of a worm detection, isolate the affected computers from the network to prevent further spread. Employ specialised malware removal tools or seek professional assistance to safely remove the worm and restore system integrity.
  • Awareness and Training: Educate employees about the risks of worm infections, emphasising the importance of safe computing practices. Teach them to identify phishing emails, suspicious links, and social engineering techniques often used by worms. That’s exactly what our Cybersecurity Training does!

Phishing, Ransomware and Business email compromise (BEC) are some common cybercriminal techniques, as per Australian Cybersecurity, that are often used by worms. We have a complete solution to protect your systems!

CONTACT US to safeguard your organisation’s digital assets!

Written By:



Latest Blogs

Send us a Message

More Posts

Report A Cyber Threat

Need help from our investigation and response team?