What is a Trojan Horse?

Published On - March 14, 2024

Trojan horses disguise as harmless apps to deceive users, stealing passwords or enabling malware access. They can disrupt systems by deleting, blocking, or altering data. Targeting Windows, Mac, and mobile devices, they spread through infected attachments, messages, or remotely. Sophisticated variants like Secret Service Trojan require no user interaction.

Examples include Pegasus for surveillance and Emotet causing significant damages. Trojans facilitate cybercrimes like backdoor installation, keylogging, banking attacks, and ransomware deployment. Vigilance and updated anti-malware software are vital defenses.

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Have you ever downloaded a program that seemed too good to be true? Well, it might be! Just like the deceitful gift that brought about the downfall of Troy, Trojan horses in the digital world are malicious programs that disguise themselves as harmless software. Now, before you panic and toss your computer out the window, let’s delve into what exactly a Trojan horse is and how to protect yourself from these digital tricksters.

How Do Trojans Work?

Trojans, unlike some other malware, rely on trickery to get installed on your device. Here’s the basic rundown of how they work:

  1. Disguise: Trojans are masters of disguise. They masquerade as legitimate software, often hiding in things like seemingly harmless downloads, attachments, or even software cracks.
  2. Delivery: Social engineering is a common tactic used by attackers to deliver Trojans. You might receive a phishing email with a malicious attachment or be lured to a fake website that tricks you into downloading a Trojan disguised as a program.
  3. Installation: Once you click or open the Trojan, it tricks you into installing it on your device. This can happen by exploiting vulnerabilities in your system or through social engineering tactics that convince you the Trojan is safe.
  4. Payload: After installation, the Trojan activates and unleashes its malicious payload. This payload can vary depending on the Trojan’s purpose. Here are some common examples:
  • Data Theft: Trojans can steal your sensitive information like login credentials, banking details, or even personal files.
  • Backdoor Access: Trojans can create a backdoor on your device, allowing attackers remote access to control your system.
  • Destructive Actions: Trojans can damage your files, corrupt your system, or even download other malware.

Trojans are particularly dangerous because they often fly under the radar. By disguising themselves as legitimate software, they can remain undetected for a long time, giving attackers ample opportunity to wreak havoc on your system.

Types of Trojans

Below are some of the most prolific types of Trojans:

Backdoor Trojans

Backdoor Trojans are among the most insidious and potentially devastating forms of malware, despite their deceptively simple nature. They facilitate the unauthorized entry of malicious software onto your system, leaving it susceptible to further attacks and exploitation. Backdoors are frequently employed to establish botnets, effectively turning your computer into a pawn within a vast network of infected devices. Furthermore, they grant attackers the ability to execute commands and codes on your device and monitor your online activities, posing a grave threat to your privacy and security.


Rootkits are malicious software programs designed to surreptitiously operate on a computer system. Their primary function is to conceal the presence and activities of other malicious programs, rendering them invisible to detection mechanisms. By doing so, rootkits enable these concealed programs to operate undetected for extended durations, granting them the freedom to compromise a system’s security and integrity without being identified.

DDoS Trojans

Distributed denial-of-service (DDoS) attacks are malicious attempts to overwhelm a target server or network with a deluge of requests. These attacks are often orchestrated using botnets, vast networks of compromised computers controlled through Trojan horses with backdoor capabilities. In June 2020, Amazon faced a formidable DDoS attack that bombarded its servers with a staggering 2.3 terabytes of data per second. The objective of such attacks is to disrupt online services and render them inaccessible, effectively cutting off access to websites and networks for a period of time.

Dropper/downloader Trojans

Emotet, a notorious malware, is classified as a dropper Trojan. Unlike conventional malware that executes code directly, Emotet serves as a delivery mechanism for more sinister payloads. It drops other malicious software, such as the banking Trojan Trickbot and the ransomware Ryuk, into infected systems. Droppers resemble downloader Trojans in their ability to deploy malware, but they differ in their architecture. Droppers encapsulate malicious components within their own package, while downloaders rely on external network resources to retrieve and install malware. Both droppers and downloader Trojans are constantly updated by their creators to evade virus scanners and expand their functionalities, making them a persistent threat to cybersecurity.

Banking Trojans

The advent of online banking has fueled the proliferation of banking Trojans. These malicious software programs target financial institutions by attempting to acquire access credentials for bank accounts. They commonly employ phishing techniques, directing victims to carefully crafted web pages that mimic legitimate bank login pages, prompting them to divulge their credentials unwittingly. To protect against these threats, it is imperative to observe sound online banking practices. Relying on secure platforms, such as the bank’s official mobile application, is crucial. Additionally, refrain from entering sensitive data on web interfaces, as they pose a higher risk of being intercepted by banking Trojans.

Fake antivirus Trojans

Fake antivirus Trojans pose a significant threat, employing deceptive tactics to manipulate users. These Trojans generate false virus detections, creating a sense of urgency and panic. Their aim is to lure users into purchasing supposedly protective software, which in reality leads to the compromise of sensitive payment data. To avoid falling victim to these scams, it is crucial to disregard virus warnings displayed when visiting websites through browsers. Instead, rely exclusively on the built-in virus scanner on your system to ensure comprehensive protection against genuine threats.

Trojan-IM (Instant Messaging)

Trojan-IM is a malicious program specifically designed to target instant messaging platforms. Its main objective is to surreptitiously acquire login credentials and passwords associated with these programs. By compromising these accounts, the malware gains access to sensitive information and facilitates the interception of communications, potentially leading to identity theft, financial loss, or other forms of cybercrimes. Notable instant messaging applications targeted by Trojan-IM include ICQ, MSN Messenger, AOL Instant Messenger, Yahoo Pager, Skype, Facebook Messenger, WhatsApp, Telegram, and Signal, highlighting the widespread threat it poses to online communication. In January 2018, Kaspersky uncovered the Skygofree Trojan, a sophisticated piece of malware which has the ability to monitor and intercept WhatsApp messages, effectively stealing these private communications from unsuspecting victims. It can also connect to Wi-Fi networks, even when the user has explicitly disabled such connections.


Trojan-Ransomware is a malicious software that infiltrates your computer, encrypting critical data. This malware targets specific data, restricting your ability to access it. The perpetrators then demand a ransom payment in exchange for restoring your computer’s performance or unlocking the blocked data. By disrupting your computer’s operation and holding your data hostage, Trojan-Ransomware exploits the fear of data loss to extort money from unsuspecting victims.

SMS Trojans

SMS Trojans have emerged as an active cybersecurity threat, despite their seemingly outdated appearance. These Trojans, such as the notorious Android malware Faketoken, employ various methods to deceive smartphone users. Faketoken masquerades as a standard SMS application, disguising its malicious activities. By sending unauthorized and costly international mass SMS messages, it can lead smartphone owners to incur substantial charges. Additionally, other SMS Trojans seek to establish connections to premium SMS services, resulting in exorbitant fees for the unsuspecting victim.


Trojan-Spy malware enables cybercriminals to covertly monitor and collect sensitive information from the infected device. Key features of Trojan-Spy include the ability to track data entered through the keyboard, capturing screenshots, and obtaining a comprehensive list of running applications. This arsenal of invasive capabilities allows attackers to spy on victims, steal passwords, financial data, and other confidential information without their knowledge or consent.

Other types of Trojans include:

  • Trojan-GameThief
  • Trojan-Mailfinder
  • Trojan-ArcBomb
  • Trojan-Clicker
  • Trojan-Notifier
  • Trojan-Proxy
  • Trojan-PSW

Examples of Trojans

  1. Emotet (2014 – Present): Emotet isn’t just a single Trojan, it’s a whole operation. This Trojan rose to infamy for its ability to morph and adapt, making it difficult to detect and eradicate. Emotet primarily spread through spam emails with malicious attachments or links. Once installed, it could steal login credentials, banking information, and even download other malware onto the infected device. Emotet was particularly disruptive because it functioned as a “downloader Trojan,” meaning it could pave the way for even more dangerous malware to infect a compromised system.
  2. ZeuS/Zbot (2007 – 2013): This Trojan specifically targeted Windows machines and was notorious for targeting financial information. ZeuS used a two-pronged approach: keylogging and form grabbing. Keyloggers record your keystrokes, which could include usernames, passwords, and other sensitive data you type. Form grabbing steals information you enter into online forms, such as banking websites. The stolen information could then be used to drain your bank accounts or sell your credentials on the dark web. Law enforcement takedowns disrupted ZeuS, but variants inspired by its design continue to circulate.
  3. ILOVEYOU (2000): This one holds the dubious honor of being one of the most damaging cyberattacks in history. ILOVEYOU masqueraded as a love letter with an attachment named “ILOVEYOU.txt.” Clicking the attachment unleashed the Trojan, which would overwrite files on the infected device and email itself to the victim’s contacts, creating a massive chain reaction. ILOVEYOU caused an estimated $8.7 billion in global damages, highlighting the potential impact of seemingly simple Trojan attacks.

How to Recognize and Detect a Trojan Virus

Trojans can be tricky to spot because they appear harmless. Here’s what to watch out for:

  • System Performance: Does your computer feel sluggish or crash frequently? Trojans can hog resources and destabilize your system.
  • Unusual Activity: Have unfamiliar applications appeared on your device? Are you bombarded with pop-up ads or experiencing strange internet behavior? These could be signs of a Trojan.
  • Security Concerns: Is your antivirus disabled or acting strangely? Unexplained data usage or outgoing connections might indicate a Trojan at work.

To detect Trojans, you can:

  • Run a scan: Use a trusted antivirus program to perform a thorough scan of your system. Consider an offline scan for an extra layer of protection.
  • Check Task Manager: Take a look at your task manager for any unfamiliar processes consuming resources.

If you suspect a Trojan infection, it’s important to act quickly. Here’s what to do:

  • Install a reputable antivirus program if you don’t already have one.
  • Consider a dedicated anti-malware scan for further protection.
  • In severe cases, seek help from a professional computer technician.

By staying alert and taking preventative measures, you can significantly reduce your risk of falling victim to Trojans.

Preventing Trojan Infections

To prevent Trojan infections, it is essential to obtain software from reputable sources, avoid opening attachments from unknown senders, disable macros in Word and Excel, and keep software updated regularly. Trojans act as “door openers”, allowing for the entry of more devastating malware. Below is a checklist to help protect you against Trojans:

  • Be vigilant about visiting suspicious websites or clicking unfamiliar links.
  • Avoid opening attachments from unknown senders or with suspicious file extensions.
  • Ensure all operating systems and applications are up-to-date to patch vulnerabilities.
  • Use a reputable antivirus software to detect and remove malicious programs.
  • Macros can be exploited by malware, so disable them unless necessary.
  • Obtain software only from trusted and reputable sources.
  • Enable file extension display to identify potentially harmful file types.
  • Use two-factor authentication and create strong, unique passwords for all accounts.
  • Schedule automated virus scans using an up-to-date scanner.

Create regular backups of your important files and store them securely.

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