TROJAN HORSE DEFINITION

Updated on October 21, 2022, by Xcitium

Trojan Horse Definition

A Trojan horse is a type of malware that disguises itself as legitimate software to trick users into installing it. Once activated, a Trojan can steal data, spy on users, create backdoors, download additional malware, or give attackers unauthorized access to a computer system.

Unlike viruses and worms, Trojan horses do not self-replicate. Instead, they rely on social engineering and user interaction to infect devices.

A Trojan Horse Definition is a malicious computer program that presents itself as legitimate software. Also called as a Trojan, it hides malware in a normal looking file.

The term Trojan horse is based on the deceptive wooden horse that led to the fall of the city of Troy in Ancient Greek mythology. The city of Troy had robust defenses that could not be broken/ penetrated by the enemy. The enemies then plotted and built a massive wooden horse that contained soldiers within its body. Troy’s gates were opened, and the horse was dragged into the city and then the gates were closed. At night, when the residents of Troy slept, the soldiers with the horse came out, opened the gates from within the city, and enabled their army to enter and destroy Troy.

The deceptive nature of this malware has led to it being defined as a Trojan horse.

Trojan Horse vs Virus

Trojan Horse	Virus
Disguises itself as legitimate software	Attaches itself to files or programs
Requires user interaction to install	Can spread through infected files
Does not self-replicate	Self-replicates and spreads
Often creates backdoors for attackers	Primarily focuses on replication
Used for data theft and unauthorized access	Often damages files and systems

While all Trojan horses are malware, they differ significantly from traditional computer viruses.

How Does a Trojan Horse Work?

A Trojan horse typically follows these steps:

The attacker disguises malware as legitimate software.
The victim downloads or installs the file.
The Trojan activates after execution.
Malicious code runs in the background.
Attackers gain access to the system or data.

Because Trojans appear legitimate, they are often difficult for users to identify before infection.

Common Types of Trojan Horse Malware

Backdoor Trojan

Creates unauthorized remote access to a system.

Banking Trojan

Steals online banking credentials and financial information.

Downloader Trojan

Downloads additional malware onto the infected device.

Spy Trojan

Monitors user activity and collects sensitive information.

Ransom Trojan

Installs ransomware that encrypts files.

Remote Access Trojan (RAT)

Allows attackers to control systems remotely.

Rootkit Trojan

Hides malicious activity from users and security software.

How Trojan Horses Infect Computers

Trojan horses commonly spread through:

Phishing emails
Malicious attachments
Fake software downloads
Cracked applications
Malicious advertisements
Compromised websites
Social engineering attacks

Users often unknowingly install Trojans because they appear trustworthy.

Signs Your Device May Have a Trojan Horse

Common symptoms include:

Slow system performance
Frequent crashes
Unexpected pop-ups
Unusual network activity
Disabled security software
Unauthorized account access
Unknown programs running
High CPU or memory usage

These indicators may suggest Trojan activity or another malware infection.

Examples of Trojan Horse Malware

Notable Trojan families include:

Zeus Trojan
Emotet
TrickBot
Dridex
QakBot
NanoCore RAT

These Trojans have been used to steal credentials, deploy ransomware, and compromise enterprise networks.

Trojan Horse vs Other Malware Types

Malware Type	Primary Purpose
Trojan Horse	Unauthorized access and data theft
Virus	Replication and file infection
Worm	Network propagation
Ransomware	File encryption and extortion
Spyware	User monitoring and information theft
Adware	Advertising and tracking

This helps users understand where Trojans fit within the broader malware landscape.

HOW ARE TROJANS HORSES SPREAD

Cybercriminals employ social engineering to spread Trojans. Victims are tricked into clicking on malicious email attachments, which look harmless. On execution, the Trojan executes itself. Drive-by downloads are another popular way of spreading Trojans. In the drive-by download method, the Trojan program automatically gets downloaded onto the device/ computer without the victim granting permission for the download. In many cases, the victim never becomes aware of the presence of the Trojan. Trojans can spread to other devices / computers that are part of the same network.

WHAT DOES A TROJAN HORSE DO?

A Trojan horse carries a malicious payload which may include a backdoor or ransomware. The backdoor would allow the controller of the malware to gain unauthorized access to system resources and data on the computer. It could allow the downloading of more malware through the backdoor. Trojans help the controller steal users’ personal information such as passwords, banking credentials, and IP addresses). Cybercriminals use Trojans to carry out ransomware attacks, and the Trojans allow the controller to spy on the victim. Trojans can delete, block, copy, and modify data, and affect the performance of the devices/computers.

TYPES OF TROJANS

A rootkit is a sophisticated type of Trojan that provides remote control of the victim’s device to the cyber criminal. Rootkits allow the victim’s device to be used as part of a botnet.

A Trojan-Banker is designed to steal account data for online banking systems, credit and debit cards.

A Trojan-Ransomware prevents the correct running of the device. It encrypts data and demands a ransom for the decrypting code.

Trojan-Spy Tprograms spy on the device when the victim is using your device/ computer

A Trojan-FakeAV is dreaded malware that attempts to threaten the victim of the presence of a malware. It offers to remove malware for an amount, while in reality the victim’s system is not affected.

In addition, there are other types of Trojans such as Trojan-Dropper, and Trojan-IM (Instant message) programs.

Xcitium Advanced Endpoint Protection is the only antivirus solution that is able to block known Trojans, and automatically contain unknown, potentially malicious files within a sophisticated virtual container, till a verdict is reached.

EXAMPLES OF TROJAN HORSE MALWARE

Xcitium Following are most famous examples of Trojan horses

Bitfrost – This is a type of Remote Access Trojan, created by the hackers intending to infect Windows Clients by modifying components.

Tiny Banker – cyber thieves developed his to extract confidential banking/financial data, while their prime targets are banks and financial institutions.

Magic Lantern – The FBI created this to log and track the Keystrokes to aid with criminal surveillance

Zeus – This is the deadliest Trojan found to date. It is a crimeware toolkit that builds its own Trojan horse that includes polymorphic versions of Trojans, drive-by downloads, and form grabbing to extract critical and sensitive information of the victim.

How to Prevent Trojan Horse Infections

Organizations and individuals can reduce risk by:

Using advanced endpoint protection
Avoiding suspicious downloads
Keeping software updated
Scanning email attachments
Enabling multi-factor authentication
Training users on phishing threats
Monitoring network activity

Preventive controls significantly reduce Trojan infection rates.

How to Remove a Trojan Horse

If a Trojan is detected:

Disconnect the infected device from the network.
Run a full malware scan.
Quarantine or remove malicious files.
Uninstall suspicious applications.
Change passwords.
Monitor accounts for suspicious activity.
Perform a follow-up scan.

Organizations may also require incident response support for severe infections.

Frequently Asked Questions

What is a Trojan horse in cybersecurity?

A Trojan horse is malware disguised as legitimate software that tricks users into installing it, allowing attackers to steal data or gain unauthorized access.

Is a Trojan horse a virus?

No. A Trojan horse is malware, but unlike a virus, it does not self-replicate or spread automatically.

What damage can a Trojan horse cause?

Trojans can steal credentials, install additional malware, spy on users, create backdoors, and compromise entire systems.

How do Trojan horses spread?

They commonly spread through phishing emails, malicious downloads, fake software, and social engineering attacks.

Can antivirus software remove Trojans?

Yes. Modern endpoint protection and anti-malware solutions can detect and remove many Trojan infections.

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