Trojan Horse Virus – Trojan Horse Malware Explained

Malware is difficult to eliminate, but it’s even more difficult when you don’t realize its presence in the first place. Trojan horse malware is a particularly difficult type of malware for this exact reason. It uses legitimate programs to covertly enter a user’s device, damaging and altering files and functions without the user’s knowledge. In this article, learn how Trojan horses work, how to detect them, and how to eliminate them from your computer.

What is a Trojan horse virus?

A Trojan horse virus, also known as a Trojan, is malicious code that seems legitimate at first glance. Much like its namesake, Trojan horse viruses trick users by appearing as secure applications; once downloaded, they load and execute malware.

Though it’s referred to as a computer virus, technically, Trojan horses aren’t viruses. Viruses can execute and replicate themselves, whereas Trojan horses need an executor. However, colloquially, “Trojan horse virus” accurately refers to Trojan malware.

How do Trojan horses work?

Trojan viruses attack the files and functions of a computer by taking advantage of weak security on a device. Because they appear as a trusted source, users download them or open them as an attachment, which installs and activates the Trojan malware. Once the Trojan is installed, it has the capacity to delete, block, modify, or copy data. Its goal is to disrupt a device performance, and it may go so far as to disrupt an entire computer network.

A Trojan horse virus on a computer

Trojans spread easily through message delivery methods like emails or text messages because they can be sent as an attachment from a falsified sender address. Users receive the messages, believe the attachments or links are safe, and download them to their devices. In doing so, the user acts as the executor.

Where do Trojan viruses come from?

Trojans disguise themselves as safe, secure programs and files, making them hard to detect. However, there are a couple of sources that are more prone to Trojans. Trojan viruses often come from:

  • Emails
  • Text messages
  • Attachments
  • File-sharing sites
  • Free WiFi networks

In order to protect yourself, use caution when interacting with these sources. Check the validity of all links before you open them, and don’t download attachments unless you are sure of what they are.

Are Trojan horses harmful?

Trojan horses are one of the most dangerous and harmful types of malware that you can have on your computer. They cause damage to files, hardware, and device data. Part of the danger of Trojan horses is that users don’t initially realize that they’re harmful, which then causes the user to allow the program to remain on their device and make changes to the system. Once they’re detected, it’s often too late to prevent damage.

Types of Trojan horse viruses

Trojan malware manifests in several forms, from backdoor Trojans operating at a distance to ransom Trojans that hold your information hostage. Familiarize yourself with these seven types of Trojans to know what to watch for.  

Backdoor Trojans

Backdoor Trojans manipulate your computer, making it a gateway for further attacks. They upload malware onto your operating system, making it vulnerable and susceptible to attacks. The malware also allows your computer to be used in future systemic attacks against other networks or devices.

Backdoors allow code or commands to be executed on your computer without your knowledge. Furthermore, they can monitor your Internet traffic and covertly glean information from your browsing history.

Distributed denial-of-service Trojans

A distributed denial-of-service attack—otherwise known as a DDOS attack—attacks a computer or system of computers by flooding the server with more requests than it can possibly handle, effectively shutting down the system.

Distributed denial-of-service attacks require several other manipulated computers, however, to deliver a successful assault. Therefore, distributed denial-of-service Trojans use a backdoor method to access a victim’s computer and set up the necessary infrastructure for future attacks.

Once activated, the infected computer can be part of a botnet in another attack. These attacks potentially render entire networks inaccessible.

Banking Trojans

One of the most common types of Trojans, banking Trojans focus on using phishing techniques to get users’ banking login credentials. Users receive emails or messages telling them then need to log in to their account, and once they log in, they’re redirected to a phishing site.

The falsified site then collects users’ information without their knowledge, allowing the hacker behind the Trojan access to the user’s account. Many banking Trojans also attempt to enter banks’ user databases to gather classified files and account information.

This is one of many reasons why using passwords only once is crucial; if a hacker gets just one of your passwords, you don’t want them to have access to all of your accounts. Many banks also recommend that users employ two-factor authentication (2FA), which safeguards their accounts with an additional login code. 2FA should be used on all accounts that allow it, not just those tied to your finances.

Downloader Trojan

A downloader Trojan installs itself into a computer system remotely. Once the device connects to the Internet, then the Trojan can download malware onto the user’s computer. Downloader Trojans are frequently sent out as seemingly-legitimate files in spam emails, but it’s the same story: once the user downloads or opens the email attachments, the downloader Trojan gets installed onto the device.

Antivirus Trojans

Antivirus Trojans present themselves under the guise of protection, falsely alerting users of viruses that are on their devices and urging them to buy an antivirus program to protect themselves. However, the antivirus program they urge users to buy is not legitimate. Instead, when users go to download the alleged antivirus software, they download malware.

If you’re alerted about a computer infection out of nowhere on the web, run a scan with an official antivirus program like Norton rather than downloading the alert’s recommended software.

Keylogger Trojans

Keyloggers, as the name implies, log every stroke you make on your keyboard and are a form of spyware. When one of these gets on your computer, the hacker can essentially monitor everything you do and collect records of everything you type. This includes all passwords, bank account numbers, email addresses, and messages.

This makes keyloggers incredibly dangerous to device users, whether you prefer a laptop or a mobile device. Keylogger Trojans aim to collect your passwords and private information for further access to your accounts.

How to detect Trojan horse viruses

Just as with any other computer malware infection, there are a few signs that indicate your computer might have a problem. Keep an eye out for these symptoms of a Trojan infection.

  • Your device runs slower than usual. Trojans use your computer’s processing power, which in turn makes your device operate at a slower rate. Trojans can cause your device to struggle with basic tasks, like opening or saving files.
  • You see an increase in pop-ups. Frequent pop-ups, whether it be on your desktop or in your browser, are a red flag.
  • Your computer shuts down or restarts on its own. Malware can change or delete files without user action, causing problems for the system. If your computer begins to behave differently, check for Trojans or other malware.
  • New or unauthorized apps appear on your computer. In many cases, Trojans download or install new files or apps to execute their tasks. If you see new or unfamiliar files, it could be from a Trojan.

If you discover any of these symptoms on your computer, it’s essential to follow up with an antivirus scan to detect any problems.

How do you get rid of a Trojan horse virus?

To get rid of a Trojan horse virus, run a scan on your computer with an antivirus program. This will alert you of any malware on your device and allow you to clear it off your device. Though this won’t fix the damage already done by the Trojan, it will prevent further damage and limit the spread of the Trojan to other files or programs.

You can also check your Task Manager or Activity Monitor, as all programs running on your computer will show up there. If you see any programs running that shouldn’t be there, you can shut them down manually.