What Is Trojan Horse? – How It Works, Uses, Types And More

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The story of the Trojan horse has been passed down through generations as a tale of cunning and deception. In the myth, the Greeks used a giant wooden horse to gain access to the city of Troy, ultimately leading to their victory in the Trojan War. Today, the term “Trojan horse” is used to describe a type of malware that operates in a similar manner. Instead of a physical horse, a Trojan horse virus is a malicious program that disguises itself as legitimate software, tricking users into downloading and executing it on their computers.

What Is A Trojan Horse Virus?

A Trojan horse virus is a specific type of malware that is designed to deceive users by appearing as harmless software or files. It often spreads through email attachments or free downloads, enticing users to open or install them. Once the Trojan horse is executed, it performs its intended malicious actions, which can vary depending on the specific type of Trojan. Some common actions include gaining unauthorized access to systems, spying on users’ online activities, or stealing sensitive data.

Unlike computer viruses and worms, Trojans do not have the ability to self-replicate. They rely on social engineering techniques to trick users into willingly installing them on their devices. This can be done through enticing email subject lines, fake software updates, or even disguised as popular applications. Once the Trojan is installed, it can operate silently in the background, making it difficult for users to detect its presence.

History Of The Trojan Horse

The story of the Trojan horse originates from ancient Greek mythology and is most famously depicted in the Aeneid by Virgil and the Odyssey by Homer. According to the myth, the Greeks, unable to breach the walls of Troy after a ten-year siege, devised a plan to infiltrate the city. They built a giant wooden horse, hiding a select group of soldiers inside.

The Greeks then pretended to sail away, leaving the horse as a gift for the Trojans. Believing it to be a peace offering, the Trojans brought the horse inside their city walls, unaware of the soldiers hidden within. Under the cover of darkness, the Greek soldiers emerged from the horse and opened the gates for the rest of their army, leading to the fall of Troy.

The term “Trojan horse” has since been used metaphorically to describe deceptive tactics used in various contexts, including the realm of cybersecurity. In the digital world, a Trojan horse operates similarly to its mythological counterpart, disguising itself as harmless software or files to gain access to a system and carry out malicious actions.

How Do Trojans Work?

Unlike computer viruses that can self-replicate and spread autonomously, Trojan horse viruses rely on user interaction to be installed and activated.

They often come disguised as legitimate-looking attachments in emails or as seemingly harmless downloads from the internet. When a user unknowingly opens or installs a Trojan, the malicious code is executed, allowing the Trojan to carry out its intended actions.

This could include gaining backdoor access to the user’s system, recording keyboard strokes to steal sensitive information like passwords or banking details, or even downloading and installing additional malware onto the infected device.

Trojans can also turn the infected device into a “zombie” computer, allowing hackers to control it remotely and use it to spread malware to other devices.

Trojans can also exploit vulnerabilities in software or operating systems to gain access to a system. They can be distributed through social engineering tactics, such as enticing users to click on malicious links or download infected files from websites or advertisements.

Uses Of A Trojan Horse

Once a Trojan horse virus becomes active on a device, it poses a significant threat to the user’s data and system security. Some of the common uses of a Trojan horse include:

1. Backdoor access:

Trojans can provide attackers with unauthorized access to a user’s computer, allowing them to control it remotely and carry out malicious activities without the user’s knowledge.

2. Keylogging:

Trojans can record keyboard strokes to capture sensitive information like passwords, credit card details, or personal information.

3. Downloading Additional Malware:

Trojans can act as a gateway for other malware, allowing attackers to install viruses, worms, or ransomware onto the infected device.

4. Ransomware attacks:

Some Trojans are designed to install ransomware, which encrypts the user’s data and demands a ransom to restore access to it.

5. Surveillance and espionage:

Trojans can activate a device’s camera and recording capabilities, allowing attackers to spy on the user’s activities and collect sensitive information.

6. Creating botnets:

Trojans can turn infected devices into part of a botnet, a network of compromised computers controlled by attackers. These botnets can be used for various purposes, such as carrying out click fraud schemes or launching distributed denial-of-service (DDoS) attacks.

7. Law enforcement activities:

In certain cases, Trojans may be used by law enforcement agencies for surveillance and gathering evidence in criminal investigations. However, this usage is highly regulated and subject to legal oversight.

Types Of Trojan

1. Backdoor Trojans:

Backdoor Trojans are designed to create a hidden entry point, or “backdoor,” into a system. This allows cybercriminals to gain unauthorized access to the compromised device or network. Once inside, they can carry out various malicious activities, such as stealing sensitive data, installing additional malware, or using the device as part of a botnet.

2. Exploit Trojans:

Exploit Trojans take advantage of vulnerabilities in software or operating systems to gain unauthorized access to a device. They typically contain code or data that targets specific weaknesses, allowing cybercriminals to exploit these vulnerabilities and compromise the device.

3. Rootkit Trojans:

Rootkit Trojans are designed to hide malicious programs or activities on a compromised device. They often modify system files and processes to conceal their presence, making them difficult to detect. Rootkits can give cybercriminals full control over the compromised device, allowing them to carry out various malicious actions without the user’s knowledge.

4. Dropper/Downloader Trojans:

Dropper and downloader Trojans are used to deliver and install additional malware onto a compromised device. Dropper Trojans act as a carrier, delivering the malware payload to the device, while downloader Trojans retrieve the malware from a remote server and install it on the device. These Trojans can be used to install ransomware, spyware, or other types of malware.

5. Banking Trojans:

Banking Trojans specifically target online banking users. They are designed to steal sensitive information, such as login credentials and financial data, from users accessing their online banking accounts. These Trojans often employ phishing techniques, tricking users into entering their credentials on fake websites or through malicious email attachments.

6. DDoS Trojans:

DDoS (Distributed Denial of Service) Trojans are used to launch large-scale DDoS attacks. These Trojans infect multiple devices, creating a botnet that can be controlled by the attacker. The botnet is then used to flood a targeted server or network with a massive volume of traffic, overwhelming it and causing it to become inaccessible to legitimate users.

7. Fake Antivirus Trojans:

Fake antivirus Trojans masquerade as legitimate antivirus software, tricking users into believing their device is infected with malware. These Trojans often display fake virus alerts and prompt users to purchase a full version of the fake antivirus software to remove the supposed threats. In reality, these Trojans are designed to steal payment information and further compromise the device.

8. Trojan-GameThief:

Trojan-GameThief Trojans specifically target online gamers. They are designed to steal user account information, such as login credentials and in-game currency, from popular online gaming platforms. These Trojans can compromise a player’s gaming account, leading to financial loss and identity theft.

9. Trojan-IM (Instant Messaging):

Trojan-IM Trojans target instant messaging applications, such as ICQ, MSN Messenger, or Skype. They are designed to steal login credentials and passwords, allowing cybercriminals to gain unauthorized access to users’ instant messaging accounts. These Trojans can be used for various malicious activities, including spreading spam or malware to the user’s contacts.

10. Trojan-Ransom:

Trojan-Ransom Trojans encrypt files on a compromised device and demand a ransom payment in exchange for the decryption key. These Trojans can render the user’s files inaccessible, causing significant disruption and financial loss.

11. SMS Trojans:

SMS Trojans target mobile devices and exploit vulnerabilities in SMS messaging systems. They can send unauthorized SMS messages to premium-rate numbers, resulting in unexpected charges for the user. These Trojans can also steal personal information from SMS messages, such as banking details or authentication codes.

12. Trojan-Spy:

Trojan-Spy Trojans are designed to spy on users’ activities on a compromised device. They can capture keystrokes, take screenshots, monitor internet traffic, and gather sensitive information, such as login credentials or personal data. The collected information is then sent to the attacker, compromising the user’s privacy and security.

13 Trojan-Mailfinder:

Trojan-Mailfinder Trojans are used to harvest email addresses from a compromised device. These Trojans can scan files, emails, and contact lists to collect email addresses, which can then be used for spamming or targeted phishing attacks.

Others includes;


This type of Trojan is designed to overload a system’s storage capacity by creating a large number of files or compressing files into a smaller size. This can cause the system to slow down or crash.


Trojan-Clicker Trojans are designed to generate revenue for cybercriminals through fraudulent clicks on advertisements. They can automatically click on ads without the user’s knowledge, generating income for the attacker.


Trojan-Notifier Trojans are used to display annoying or malicious pop-up notifications on the infected device. These notifications can contain advertisements, fake security alerts, or links to malicious websites.


Trojan-Proxy Trojans create a proxy server on the infected device, allowing attackers to route their internet traffic through the compromised device. This can be used to hide the attacker’s identity or carry out malicious activities while appearing to come from the infected device.


Trojan-PSW Trojans are designed to steal passwords and login credentials from the infected device. They can capture keystrokes, take screenshots, or monitor network traffic to gather sensitive information.

Trojans As A Threat To All End Devices

Trojan horse viruses have evolved to become a threat not only to Windows computers but also to Mac computers and mobile devices.

This means that users of all types of devices should be cautious and ensure they have up-to-date anti-malware protection installed, such as Kaspersky Internet Security.

Malware can find its way onto devices through various means, including infected email attachments, manipulated text messages, or fake websites.

In some cases, Trojans can even be installed remotely on target systems without the user’s knowledge or interaction.

For example, Pegasus software developed by NSO is distributed through the mobile phone network and can provide powerful interception capabilities, allowing the attacker to gain complete access to the device, record calls, or use the phone as a listening device.

In some cases, even law enforcement agencies use Trojans for surveillance purposes, but only with proper legal authorization.

Cybercriminals want to cause maximum damage with Trojans:

While state surveillance Trojans may be used for tracking and punishing criminal offenses, cybercriminals have a different motive – personal enrichment at the expense of their victims.

They employ various programs and malware chains to achieve their goals. For example, a backdoor Trojan can be installed on a computer through an infected email attachment, allowing further malware to be silently loaded onto the system.

This can include keyloggers that record keystrokes, banking Trojans that steal financial data, or ransomware that encrypts the entire computer until a ransom is paid. One notorious Trojan is Emotet, which is often described as the “most destructive malware.”

Emotet spreads through spam emails and infected Word or Excel documents, targeting mainly companies but also affecting private users by accessing their email addresses and adding them to its database. The damage caused by Emotet can amount to millions of dollars.

Piggybacking onto the end device:

Trojans can also be distributed by “piggybacking” on seemingly free programs. It is crucial to avoid downloading software from dubious sources, such as codec packs or cracked programs, as the damage caused by Trojans can far exceed any potential savings.

It is important to note that a Trojan should not be confused with a virus. While viruses can replicate independently, Trojans are merely a means to open a door for potential attacks, but the consequences can be devastating.

Examples Of Trojan Horse Virus Attacks

1. Zeus or Zbot:

Zeus is a well-known Trojan that primarily targets financial institutions. It is a toolkit that allows hackers to create their own Trojan malware. Zeus is designed to steal sensitive information, such as login credentials and financial details, by utilizing techniques like form grabbing and keystroke logging. The stolen data can then be used for fraudulent activities, such as unauthorized access to bank accounts or identity theft.

2. Ransomware Trojans:

Ransomware Trojans, such as WannaCry and Petya, have caused significant damage worldwide. These Trojans encrypt the files on a victim’s computer or network, making them inaccessible until a ransom is paid. Ransomware attacks can have severe consequences for individuals, businesses, and even government organizations, leading to financial losses and data breaches.

3. Emotet:

Emotet is a highly sophisticated and versatile Trojan that has been active since 2014. It is primarily spread through spam emails and infected attachments. Once a system is infected, Emotet can download additional malware, steal sensitive information, and propagate itself within the network. Emotet has been responsible for massive financial losses, with estimates running into the millions of dollars.

4. Tinba:

Tinba, also known as Tiny Banker, is a banking Trojan that specifically targets financial institutions. It is designed to intercept and steal banking credentials, credit card information, and other sensitive data entered by users on compromised websites. Tinba is known for its small size and advanced evasion techniques, making it difficult to detect and remove.

5. SpyEye:

SpyEye is a Trojan that targets online banking systems and steals sensitive information. It can perform various malicious activities, such as capturing keystrokes, taking screenshots, and injecting malicious code into web pages. SpyEye has been responsible for significant financial losses and has affected numerous individuals and organizations worldwide.

Is A Trojan Horse A Virus Or Malware?

A Trojan horse is a type of malware, but it is not a virus. Unlike viruses, Trojans cannot replicate themselves or propagate without the assistance of the end user. Trojans rely on social engineering tactics to deceive users into executing them.

The term “Trojan horse virus” is often used colloquially, but it is technically incorrect. Trojans can take on various forms and serve different purposes, such as acting as standalone malware or facilitating other malicious activities, such as delivering payloads, enabling system vulnerabilities, or establishing communication with the attacker.

Trojans are a subset of malware, which encompasses a wide range of malicious software designed to exploit or harm computer systems.

How To Recognize A Trojan Virus

1. Sudden Changes in Computer Settings:

One of the signs that your computer may be infected with a Trojan virus is if you notice sudden changes in your computer settings. This could include changes to your desktop background, browser homepage, or default search engine. Trojans often modify these settings to redirect you to malicious websites or display unwanted advertisements.

2. Decreased Computer Performance:

Another indication of a Trojan virus is a noticeable decrease in your computer’s performance. If your computer suddenly becomes slow, freezes frequently, or crashes unexpectedly, it could be a result of a Trojan infection. Trojans consume system resources and can cause your computer to run sluggishly.

3. Unusual Activity:

Pay attention to any unusual activity taking place on your computer. This could include unexpected pop-up windows, new icons appearing on your desktop, or unfamiliar processes running in the background. Trojans often perform malicious activities without the user’s knowledge, so any suspicious behavior should be investigated.

To confirm the presence of a Trojan virus, it is recommended to use a reputable Trojan scanner or malware-removal software. These tools can scan your computer for known Trojan signatures and help identify and remove any infections.

How To Remove A Trojan Horse

If a Trojan horse is detected on your computer, it is crucial to take immediate action to prevent further damage. Here are the steps to remove a Trojan horse:

1. Disconnect From the Internet:

As soon as you identify a Trojan horse, disconnect your computer from the internet to prevent the malware from communicating with its command-and-control server or spreading to other devices on your network.

2. Use Antivirus or Antimalware Software:

Run a full system scan using an updated antivirus or antimalware program. These security tools can detect and remove Trojan infections from your computer. Follow the prompts provided by the software to quarantine or delete the infected files.

3. Reinstall the Operating System (if necessary):

In some cases, the Trojan horse may have caused significant damage to your operating system, making it difficult to completely remove the infection. If this happens, consider reinstalling your operating system to ensure a clean start. Remember to back up your important files before proceeding with the reinstallation.

It’s important to note that removing a Trojan horse can be a complex process, and it may require advanced technical knowledge. If you’re unsure about how to proceed, it’s recommended to seek assistance from a professional computer technician.

How To Protect Against A Trojan Horse

Prevention is key when it comes to protecting your computer from Trojan horse infections. Here are some measures you can take to safeguard your system:

1. Exercise Caution With Email Attachments:

Avoid opening or downloading email attachments from unknown or suspicious sources. Even if the email appears to be from someone you know, be cautious as their account may have been compromised. Delete any suspicious emails without opening them to prevent Trojan infections.

2. Install And Update Internet Security Software:

Install a reputable internet security suite that includes antivirus and antimalware protection. Keep the software up to date to ensure it can detect and block the latest Trojan threats. Set up regular scans to detect and remove any potential infections.

3. Keep Your Operating System Updated:

Regularly update your operating system with the latest security patches and updates. Software vulnerabilities can be exploited by Trojans to gain access to your system. Enabling automatic updates can ensure you stay protected against known vulnerabilities.

4. Use Strong And Unique Passwords:

Protect your personal accounts by using strong, unique passwords that include a combination of letters, numbers, and symbols. Avoid using easily guessable passwords or reusing passwords across multiple accounts. This can help prevent unauthorized access to your accounts and reduce the risk of Trojan infections.

5. Practice Safe Browsing Habits:

Be cautious when visiting websites and avoid clicking on suspicious links or pop-up ads. Use internet security software that can identify safe websites and warn you about potentially harmful ones. Stick to trusted websites for downloading software and avoid downloading programs from unverified sources.

6. Regularly Back Up Your Files:

Create regular backups of your important files to an external storage device or cloud storage. In the event of a Trojan infection or any other data loss incident, having backups will allow you to restore your files without paying a ransom or losing valuable data.


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