A Trojan horse is a software package containing malicious code that appears legitimate, similar to the ancient Greek myth of the deceptive trojan horse in the Odyssey that caused severe damage despite having a harmless exterior. This article explains the meaning of Trojan horse cyber threats, their various examples, real-world attacks, and best practices to protect against Trojan-driven cybercrime.
Table of Contents
What Is Trojan Horse?
A Trojan horse (or simply known as Trojan) is defined as a software package containing malicious code that appears to be legitimate, similar to the ancient Greek myth of the Odyssey that caused severe damage to Troy despite having a harmless exterior.
Trojans are malicious code or software that infiltrate a computer while impersonating a genuine program and eventually take over the system without the user or IT administrator noticing. Technically, Trojans are not viruses – instead, they are a sort of malware. Although this is incorrect, the terms Trojan malware and Trojan virus are frequently used interchangeably. Viruses can execute and replicate themselves. A Trojan, however, cannot and must be executed by the user.Â
One can find the original narrative of the Trojan horse in Virgil’s Aeneid and Homer’s Odyssey. In the story, the invaders of the city of Troy were able to enter the city gates by using a horse disguised as a gift. The warriors hid inside the massive wooden horse, then climbed out and allowed the other soldiers in once they were inside the gates. Similarly, a Trojan horse can effectively bypass the otherwise strong defenses protecting a system. The Trojan malware takes control of your computer, potentially leaving it susceptible to other “invaders.â€Â
Trojans can be employed to perform several harmful actions like data deletion, data censorship, data modification, data copying, and causing interference in the operation of computers or computer networks.
See More: What Is a Security Vulnerability? Definition, Types, and Best Practices for Prevention
How do Trojans attack?
A Trojan horse, unlike computer viruses, cannot manifest on its own. It requires a user to download the client-side of the application for it to function. The executable (.exe) file must be implemented and the software installed for the Trojan to attack the device.
Trojans operate by impersonating legitimate files to deceive victims into clicking, opening, or installing them. When this occurs, the Trojan proceeds to install malware on the device and runs every time the infected device is switched on. Email Trojans, for example, use social engineering tactics to resemble harmless email attachments, fooling the user into opening the attached file.
A Trojan malware-infected machine can also transfer it to other systems. A cybercriminal transforms the system into a zombie computer, giving them remote control over it without the user’s knowledge. Hackers can then use the zombie computers to spread malware across a network of devices known as a botnet.
The malware will activate upon the performance of specific actions by the user, such as accessing a particular website or using a banking app. Based on the Trojan type and its creation method, the infection may erase itself, revert to a dormant state, or stay active even after the hacker’s desired action is completed.Â
See More: What Is Cyber Threat? Definition, Types, Hunting, Best Practices, and Examples
Examples of Trojan Horse Virus: 10 Key Types
Here are ten key examples of Trojan horses (keep in mind that although these are not self-replicating viruses, the malware types are commonly referred to as Trojan horse viruses):
Examples of Trojan Horse Virus
1. Backdoor Trojans
As the name implies, this Trojan can create a “backdoor†on a computer to gain access to it without the user’s knowledge. A backdoor Trojan allows an attacker to acquire remote access to control a computer, typically uploading, downloading, or executing data at will. These are one of the most basic yet potentially harmful varieties of Trojans. They are primarily used to install new malware, spy on you, and steal your data. Furthermore, a backdoor Trojan is often used to establish a botnet via a network of zombie computers – used in large-scale attacks.Â
2. Distributed Denial of Service (DDoS) attack TrojansÂ
Distributed Denial of Service (DDoS) type Trojans are developed solely to recruit your device into a botnet, a network of linked devices remotely controlled by a hacker known as a bot herder. Such malicious programs are intended to launch a DDoS attack from an infected computer to a pre-specified IP address. The goal is to bring a network down by flooding it with traffic. This traffic is generated by your infected computer and others like it.Â
Numerous forms of DDoS attacks target both the network and application layers. You could categorize them based on their influence on the targeted computing resources by saturating bandwidth, using server resources, exhausting an application, or on the nature of the targeted resources:Â
- Attacks against network resources: Trojans causing user datagram protocol (UDP) floods, internet control message protocol (ICMP) floods, and internet group management protocol (IGMP) floods
- Attacks against server resources: Trojans impacting transmission control protocol/internet protocol (TCP/IP) flaws, TCP reset attacks, and low and slow attacks such as Sockstress and secure sockets layer (SSL) attacks, the detection of which is challenging
- Attacks against application resources: Trojans causing hypertext transfer protocol (HTTP) floods, domain name system (DNS) floods, and other low and slow attacks such as Slow HTTP GET requests (Slowloris) and Slow HTTP POST requests (R-U-Dead-Yet)Â
3. Fraudulent antivirus TrojansÂ
Phony antivirus Trojans are another example of a particularly devious variety. A fake antivirus Trojan mimics the functions of genuine antivirus software and is designed to detect and eliminate dangers in the same way that a real antivirus program does. But it extorts money from users for removing threats that may or may not exist. When users pay for these services, their payment information is sent to the Trojan’s creator for further misuse. In a nutshell, unexpected virus warnings in the browser while visiting a website are best left unattended. You should trust only legitimate and system-provided virus scanners.Â
4. Downloader TrojansÂ
A Trojan-downloader is a sort of Trojan that installs itself on the system and then connects to a remote server or website to download more applications (typically malware) onto the affected machine. This Trojan is designed to infect a computer even more than it already is. It downloads and installs new versions of malicious applications.Â
Trojans and adware are examples of such threats. Trojan downloaders are also often distributed in disguised file attachments in spam emails. As a simple form of social engineering, the linked programs are often labeled with legitimate-sounding program or document titles, such as “invoice.exe†or “accounts.exe.†Once the file attachment is opened, the trojan-downloader is installed onto the system.Â
5. Mailfinder TrojansÂ
A mailfinder Trojan seeks to harvest and steal email addresses saved on a computer and sends them to the criminal users via email, the web, file transfer protocol (FTP), or other methods. Cybercriminals then utilize stolen addresses to send out large, bulk-based mailings of malware and spam.Â
6. Rootkit TrojansÂ
Rootkits are meant to conceal specific activities or items in the system. Their primary goal is to prevent the detection of malicious tasks to extend the time the programs can function on the machine, resulting in maximum damage.Â
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7. Remote Access TrojansÂ
Remote access Trojan (RAT) is malware that enables attackers to control infected machines remotely. Once the RAT is installed on a compromised machine, the attacker can transmit commands to it and receive data in response. These Trojans are among the deadliest since they create countless opportunities for remote access to the compromised system.Â
The RAT will establish a command and control (C2) connection with the attacker’s server to deliver commands and data to the RAT. RATs typically have a set of built-in commands and mechanisms for concealing their C2 communication. Installation and removal of programs, data reading from the keyboard, file manipulation, clipboard monitoring, and webcam hijacking are all standard RAT capabilities.Â
8. Ransomware TrojansÂ
This sort of Trojan alters data on the victim’s computer so that the victim can no longer use it or hinders the computer from functioning correctly. The user receives a ransom demand once the data has been “taken hostage†(restricted or encrypted) by the ransomware Trojan. The ransom demand instructs the victim to send money to the malicious user; upon receipt, the cybercriminal sends the victim a program to restore the victim’s data or computer’s performance.Â
9. Short message service (SMS) TrojansÂ
An SMS Trojan infects mobile devices (usually Android) and can send and intercept text messages. This involves sending messages to high-cost phone numbers, which raises the cost of a user’s phone bill. SMS Trojans can operate in a variety of ways. For example, Faketoken transmits mass SMS messages to premium overseas lines while impersonating a typical SMS app. The owner of the smartphone has to bear the cost of this. Other SMS Trojans connect to high-priced premium SMS services to incur an unexpected bill.Â
10. Banking TrojansÂ
Banking Trojans are ubiquitous examples of malware. This Trojan type targets online activities and personal information used for banking. Given the growing popularity of online banking and the carelessness of bank account holders, this is a viable approach for cyber-attackers to obtain funds quickly. The Trojan horse installs on the user’s system and looks like a regular program. Once the user clicks on it, it is activated and will trigger a series of phishing tactics. Banking Trojans often employ phishing techniques, such as redirecting victims to bogus pages where they are meant to input their access credentials.Â
See More: What Is Endpoint Security? Definition, Key Components, and Best Practices
Examples of Trojan Horse AttacksÂ
Now let us discuss a couple of notable examples of real-world cyber-attacks that were carried out using Trojan horses.Â
The first is the Emotet malspam-causing Trojan horse. Emotet was first identified in 2014 as a banking Trojan. However, as hackers began utilizing it to distribute other malware instead, Emotet caused quite a stir in the cybersecurity world and is widely regarded as one of the most dangerous malware strains ever developed. It targeted both corporate and individual victims through enormous spam and phishing campaigns.Â
The malware was used to construct many botnets, which were then rented out to other cybercriminals under a malware as a service (MaaS) model. Emotet was finally brought down in 2021 due to a global law enforcement effort.
Another example of Trojan horse attacks that caused unprecedented damage was the ZeuS or Zbot Trojan horse on Microsoft Windows, active from 2007 to 2013. The ZeuS Trojan initially surfaced in a data theft attempt on the United States Department of Transportation in 2007. ZeuS, which is primarily a banking Trojan, is commonly used to steal financial information via two browser-based techniques:Â
- Keylogging occurs when the Trojan records the keystrokes as users type information into their browser.
- ZeuS can intercept the username and password through form grabbing when users log in to a website.
ZeuS infected millions of machines after being spread mainly through phishing emails and automatic drive-by downloads on infected websites, and as a result, was used to construct Gameover ZeuS, one of history’s most notorious botnets. Interestingly, it targeted Microsoft Windows by exploiting a vulnerability in several operating system versions.Â
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Preventing Trojan Horse Attack: Top 10 Best Practices for 2022Â
A Trojan horse can typically lurk on a device for months or even years before the user realizes it has been infected. Some of the telltale indicators of infection are as follows:Â
- Poor device performance: If a computer or mobile device is running slowly or crashing more frequently than usual, it may be a sign of undetected Trojan malware or other malicious programs.
- Strange device behavior: This may involve executing programs without the user’s intervention. An increase in the number of spam messages and pop-ups on the gadget can also indicate a Trojan attack.
To prevent such attacks from impacting your system, you can follow ten best practices:Â
1. Never open an email attachment from an unknown sourceÂ
Trojans require the user’s authorization to run on the computer – i.e., the user must either start the program themselves or open a file that subsequently operates the program. As a result, the first and ideal defense against Trojans is never to open email attachments or launch a program if you are not sure of the source. This includes files acquired via websites or peer-to-peer programs.Â
2. Keep all software systems up to dateÂ
This is especially true for the operating system, browser, and built-in cybersecurity software like Windows Defender. Hackers leverage known security flaws that can aid the Trojan in performing, and even if a vendor sends out software patches, it will not help until the user keeps the updated version of the software.Â
3. Always keep a firewall enabledÂ
It is best to maintain a firewall in an active state at all times to secure your Internet connection. Firewalls – both firewall software and firewall hardware – are excellent at stopping malicious internet traffic and may routinely prevent Trojans from being downloaded to the computer. Organizational IT administrators, in particular, should install effective firewall systems that protect enterprise networks and connected endpoints from malicious traffic that may contain Trojan horses.Â
4. Regularly backup data
If one’s computer becomes infected with a Trojan horse, regular data backup aids in the restoration of the data. It is advisable to encrypt all of the data so that if it is stolen or lost, it has a high probability of remaining secure.Â
5. Avoid third-party downloadsÂ
A user should avoid visiting websites by clicking on shortened URLs at all costs – instead, it is better to enter the website address into the address bar. It is not a good idea to download software from unknown publishers. Furthermore, it is critical to exercise extreme caution while entering credit card information on a website. Users should obtain the software packages from original vendors or official portals such as the Apple App Store and Google Play. Although Trojans have hacked these in the past, they are far safer than alternative options.Â
See More: What Is a Firewall? Definition, Key Components, and Best Practices
6. Learn how harmful applications appearÂ
If one suspects that their system has gotten slow or that some apps appear suspicious, it is always helpful to know what the problem is. It could be a worm, a virus, a Trojan horse, or anything else. A basic understanding of what they look like and what they do can help in this situation. For example, JS.Debeski.Trojan is a Trojan horse, and with some research, users can educate themselves on the file names and file types that usually signal a Trojan attack.Â
7. Install a good antivirusÂ
Trojans will automatically be kept off the computer if a powerful antivirus tool from a respected vendor is being used. It is best to choose one that also functions as a malware protection software tool, capable of detecting and removing Trojans and other infections from devices.Â
8. Utilize an ad blocker and a safe browser
Some Trojans spread via infected web advertisements. An ad blocker or private browser will prevent these and other potentially fraudulent advertisements from loading in the browser, ensuring that infected websites do not infiltrate the user’s system with a Trojan.Â
9. Avoid clicking on web banners or unknown URLsÂ
Malvertising, the use of online advertising to spread malware, typically works via drive-by downloads. For example, some malware developers create websites that can automatically install Trojan horses onto the device as soon as one visits them, or when a user clicks on the cross button to close a pop-up. However, it initiates a download instead. By avoiding unknown websites, you lower your chances of installing a Trojan.Â
10. Be aware of phishing attacks and password-related risksÂ
Phishing is a type of social engineering attack widely used to obtain user information, such as login credentials and credit card details. Similarly, phishing may also be used to install a Trojan on your system. It involves an attacker pretending to be a trustworthy entity and urging the victim to open an email, instant message, or text message, which activates the Trojan horse. Hence, one must avoid opening an attachment in an email that an unknown user has delivered.
 Also, It is recommended to use complicated, one-of-a-kind passwords to secure your accounts. You can create a unique password for each account, combining letters, numbers, and symbols. Storing passwords in your browser may make them vulnerable to Trojan attacks, where the malware uses techniques like keylogging to extract confidential information.
See More: Top 10 Anti-Phishing Software in 2021
TakeawaysÂ
Trojans refer to any malware that appears to be a legitimate file but installs a harmful software package on your system instead. They may cause damage in various ways, and Trojan horses are also frequently sold or leased out on the dark web – which further extends the attack’s impact. Crimes caused via Trojan horses range from one-off attacks that infect a single-user system to large-scale global attacks that spread the infection through known system vulnerabilities. Consequently, it is essential to stay vigilant, avoid suspicious websites and software vendors, and maintain robust and up-to-date systems.
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