Worms vs Trojan Horse Viruses: Key Differences, How They Spread, and How to Stay Protected

Of all the malware lying in wait to infect unsuspecting devices, Trojan horses and worms are some of the more common and well known. These terms are often used interchangeably, but Trojans and worms each have unique characteristics and behaviors. Let’s break down some of the differences so you can understand how a worm is different from a Trojan and explore how they spread, attack, and – most importantly – how to prevent them. 

What is a computer worm?

A computer worm is a self-replicating malware program that spreads through networks without the need for a host file. It worms its way into systems, exploiting vulnerabilities in systems and propagating independently, often infecting a large number of devices around a network. Unlike other types of malware, worms don’t rely on user interaction or even a host file in order to be able to spread and replicate themselves.

Their key characteristics are the fact that they are self-replicating and don’t need a host.

Worm behavior and consequences

• Slowing down systems and consuming bandwidth
• Exploiting system vulnerabilities and installing additional malware
• Deleting or corrupting files and disrupting normal operations
• Infecting other systems on the same network
• Allowing cybercriminals to gain access to sensitive information

What is a Trojan horse virus?

A Trojan horse virus is a type of malware that disguises itself as legitimate software in order to trick people into downloading or installing it. The concept is based on the myth of the Greek soldiers using a giant wooden horse to sneak into the city of Troy during the Trojan War. Worms are a subset of Trojan horse; unlike worms, Trojans can’t replicate on their own. They can, however, open backdoors that allow unauthorized access to perform malicious tasks.

Their key characteristics are that they need help to spread, and disguise themselves as legitimate software.

Trojan behavior and consequences

• Deceiving users into installing or downloading them
• Stealing sensitive information, such as passwords and financial information
• Creating backdoors to allow future access to the device, compromising system control
• Installing additional malware to perform harmful actions and deleting files

Worms vs Trojan horses – the key differences

Similarities between computer worms and Trojan horse viruses

While they are two distinct types of malware that use different methods, worms and Trojans do have their similarities.

• Malicious intent – both are designed to cause harm.
• Damage potential – both can lead to data theft and damage.
• Exploitation of vulnerabilities – both exploit software and vulnerabilities.
• System resource of impact – both slow down systems.
• Can be used for remote control – both can allow attackers to remotely control a device.
• Infiltration – both can enter systems through phishing and downloads.
• Association with other malware – both can work in tandem with other types of malware.
• Prevention – both can be blocked and prevented by proper security practices.
• Need for security awareness – both can be identified through proper security vigilance.

Examples of worm attacks

ILOVEYOU (2000)

One of the most famous examples of a worm, the ILOVEYOU worm spread via email attachments, infecting millions of computers across the globe. It resulted in widespread data loss and billions of dollars in damages.

Code Red (2001)

The Code Red worm exploited a Microsoft vulnerability, infecting over 300,000 servers in just 14 hours. Its rapid spread significantly impeded internet traffic.

Mydoom (2004)

The fastest-spreading email worm, Mydoom infected millions of systems worldwide. Its effects included opening backdoors for remote access and initiating distributed denial-of-service (DDoS) attacks.

Examples of Trojan attacks

Zeus Trojan (2007)

The Zeus Trojan targeted banking information by logging keystrokes and stealing passwords. It infected thousands of computers, leading millions of dollars in financial losses.

Emotet Trojan (2014)

Initially a banking Trojan, Emotet evolved into a highly destructive malware that spread rapidly through phishing, stealing sensitive data and installing other malware.

CryptoLocker Trojan (2013)

The CryptoLocker Trojan encrypted users’ files and demanded ransom payments in exchange for decryption keys, leading to widespread financial loss and compromised data.

Prevention and security measures

Being proactive with your cybersecurity can help to prevent malware such as worms and Trojans from gaining access to your devices. Here are some recommended steps you can follow to significantly reduce the risk of a malware infiltration.

Always use unique passwords

Ensure all accounts and systems use strong, unique passwords to minimize the risk of unauthorized access.

Keep software and operating systems up to date

Stay on top of updates, as they will patch any existing vulnerabilities that worms and Trojans often exploit.

Use Firewalls and Intrusion Detection Systems (IDS)

These tools can help to monitor your network and block suspicious traffic, preventing worms and Trojans from gaining access to your system.

Increase your awareness and use filters

Being able to recognize phishing attempts and filtering your emails can help to prevent you falling victim to malicious attachments and links.

Network segmentation

Separating networks can prevent worms from spreading freely between them if one system is compromised.

Using Trojan scanner tools

Use a reliable Trojan scanner to regularly check for malware infections. Consider using our free Trojan scanner and removal tool to help detect and remove any malicious software.

All malware great and small

An easy way to remember the difference between worms and Trojans are that worms can crawl on their own – Trojan horses need to be pushed. Similarly, worm viruses can move and replicate independently, whereas Trojan horses need user interaction in order to spread. 
By staying vigilant and employing robust security measures, you can keep any and all malware at bay. Don’t wait until it’s too late – protect your system today by staying informed and using the right tools.