What Is a Trojan Horse?

Cybersecurity is always a top priority for any organization because some threat actors can get sneaky with their attacks. One example is a Trojan Horse that this article will discuss. Let’s see how a Trojan Horse works, how dangerous it can be, and how to protect yourself from falling victim to its deception.

What is a Trojan Horse?

A Trojan Horse is a type of malware that cleverly disguises itself as legitimate software, documents, or other seemingly harmless files. This allows unsuspecting victims to be tricked into installing the Trojan Horse on their computers or other devices. Once installed, the Trojan Horse can steal data, install other malware, or disrupt the device’s operation.

How does a Trojan Horse work?

Trojan Horse is deceptive malware that tricks victims into thinking that it is legitimate software that’s safe to install. One of the most common scenarios in which Trojan Horses start their attack is through phishing emails. These emails may appear to come from a trusted source and usually contain attachments and links that seem harmless at first glance.

Once the email recipient opens the attachment or clicks on the link, they will be tricked into unknowingly downloading and installing the Trojan Horse. This can happen in various ways, such as the following:

1. The attachment itself is a Trojan Horse:

Trojan Horses can disguise themselves into different file formats such as executable files (.exe), images (.jpg, .png), documents (.docx, .pdf), scripts (.js), or installers specific to the device’s operating system (.apk).

When a recipient clicks on the attachment, the Trojan Horse either presents them with a fake installation window or triggers a hidden script that downloads and installs the Trojan without any user notification.

2. The link leads to a malicious website:

Bad actors can also create a legitimate-looking website to which the attached link from a phishing email would lead. Since the website looks trustworthy if not examined thoroughly, some people could be tricked into downloading files from these websites without knowing that they are already downloading a Trojan Horse.

3. The link might exploit vulnerabilities in the user’s software:

In some cases, clicking a malicious link might exploit security holes in the user’s web browser or operating system to automatically install the Trojan without any user interaction.

An overview of the term “Trojan Horse”

The term Trojan Horse was directly derived from ancient Greek mythology about the wooden horse that the Greeks said to have used to enter the city of Troy, which ultimately led to the city’s downfall. The sneaky nature of the malware is similar to the Trojan Horse’s deceptive role in the myth. Just as the Greeks hid inside the wooden horse to gain access to Troy, a Trojan Horse disguises itself as harmless software to infiltrate a computer system.

Notable Trojan Horse attacks

Here are some of the most notable Trojan Horse attacks throughout the history of computing:


Also known as the “Love Letter” or “Love Bug,” the ILOVEYOU attack in 2000 was executed using a computer worm disguised as a love letter. ILOVEYOU’s point of origin was Manila, Philippines. The attack started in the form of an email with the subject “ILOVEYOU” containing an attachment “LOVE-LETTER-FOR-YOU.TXT.vbs.”

At that time, Windows hid file extensions by default, making the “.vbs” (a script) extension invisible to users. This tricked unsuspecting victims into thinking the attachment was just a normal text file, so they double-clicked it, allowing their computers to run the malicious script. ILOVEYOU also emailed itself to the victim’s address book, further spreading the infection.

  • Zeus

Zeus is a malware that targets Windows computers and is used to obtain banking information through keylogging and form grabbing. It was discovered in 2007 and became widespread in 2009, compromising over 74,000 FTP accounts in the process.

  • Stuxnet

Stuxnet is a computer worm first discovered in 2010. The Trojan Horse was thought to have been created jointly by the US and Israel and was responsible for damaging Iran’s nuclear program.

Trojan Horse vs virus

Some mistake the Trojan Horse as a form of computer virus. However, there is a significant difference between the two. As explained, a Trojan Horse is a type of malware that disguises itself as legitimate software, documents, or files. A Trojan Horse needs to be installed to function by deceiving users into clicking links, downloading files, or installing seemingly harmless software.

Meanwhile, a computer virus is another type of malware that can replicate itself and spread from one computer to another. It doesn’t need any user interaction to spread and can corrupt files directly, making it potentially more contagious and widespread.


Trojan Horses’ deceptive nature is one of its harmful characteristics. This enables users to fall victim to malware attacks, get their data stolen, have the Trojan Horse install other malware in their computer system to cause further damage, and more. That’s why it’s important to educate computer users about caution when opening attachments, identifying malicious emails, clicking on random links, and many more ways Trojan Horses may infiltrate devices.

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