A Trojan is a kind of malware that poses as a legitimate program to infiltrate and infect user devices. It derives its name from the famous Trojan horse attack used by the Greeks to invade the city of Troy.
Trojans spread through several means, including:
- Emails
- Links
- Fake websites
- App or game downloads
- Torrents
They often use social engineering to lure people into downloading malicious programs.
Once Trojans infect a device, they can cause different kinds of harm, such as stealing personal data, encrypting files, and installing other kinds of malware.
Trojans are often hard to detect and can stay on devices without the user knowing. However, some telltale signs of Trojan malware infection include:
- Frequent pop-ups
- The slowing down of your device
- The presence of unfamiliar files and programs
Given the damage Trojans can cause, it’s best to take steps to prevent an infection in the first place. One easy way to do this is to use a reliable antivirus software provider like Bitdefender.
Read the rest of the article for more information on the kinds of Trojan malware and the steps involved in removing them from your device.
A Trojan virus can cause serious issues to your device. It aims to gain access to your system and compromise essential functions. Trojan malware has the ability to steal your information and modify or completely delete it. However, Trojans cannot make copies of themselves, like computer viruses and worms.
In this comprehensive guide, we will explain how a Trojan works, what the different kinds of Trojans are, and how you can identify and prevent them.
What Are Trojans?
A Trojan or Trojan horse virus is a malicious piece of software designed to enter and compromise a computer or device without the user’s knowledge or permission. It can spread and infect machines via multiple channels, including spam emails, infected websites, and software downloads.
The term “Trojan” comes from the ancient Greek myth of the Trojan Horse, where the Trojans were deceived by the Greeks into bringing a great wooden horse packed with enemy soldiers into their city, believing it to be a gift. Similarly, a Trojan virus disguises itself as a genuine or beneficial program, but it is actually a tool cybercriminals use to obtain access to a device and steal valuable data or damage its functionality.
Are Trojans viruses?
We’re sure you’ve heard the term “Trojan virus” quite frequently. However, technically, Trojans are not true viruses because they can’t self-replicate. This doesn’t mean Trojans aren’t harmful, however. There are different kinds of malicious code that can affect your device, such as:
| Type of malicious programs | Description |
|---|---|
| Worms | Computer worms contain malicious code or software and spread between devices by themselves. This means no human interaction is required to initiate a worm infection: it will automatically detect other devices to spread to the network. |
| Viruses | A computer virus consists of malicious code that attaches itself to a file. When the file is executed, the virus is triggered and can self-replicate on the device. However, human action is necessary to initiate the infection, making it different from a worm. |
| Trojan malware | A Trojan also requires active human intervention to trigger its spread but doesn’t self-replicate. On top of that, the key difference between a Trojan and a virus is that a Trojan disguises itself as a legitimate program, and a virus does not. |
In short, while Trojans and viruses are both part of the same family, namely “malware,” they function slightly differently.
Where Do Trojan Viruses Come From?
Trojan viruses can originate from a wide range of sources. They will most likely look like normal, harmless software to trick you into installing them, so they can infect your computer. You’re most likely to come across Trojan malware in the following places.
1. File-sharing websites
Many people use file-sharing websites to download a new movie or stream their favorite show. These sites are also often used to share software programs illegally through torrents.
Hackers looking for a way to gain easy access to your computer often use these torrenting sites. So, when you download a torrent file, you unknowingly also download Trojan malware to your device. If you can’t avoid using torrenting sites, you must ensure that you can protect yourself against potential hacker attacks.
2. Phishing emails
Phishing emails have become an everyday normality. Even most internet users that are not tech-savvy will have had some experience with fake emails. These messages in our inboxes might pretend to be sent by their bank or another legitimate-looking service, asking for passwords or account information. This is another popular way used to spread Trojans.
The most obvious signs of a phishing email include:
- A very generic greeting like “Dear User”
- Spelling mistakes within the body text
- A service logo or email layout that doesn’t look quite right
- A request to click a link to update payment details
If you get an email or text message like that, you shouldn’t click on any links included in that message. With one click, you might just download a Trojan onto your device.
Some phishing emails may look very legitimate. A 2022 PayPal phishing scam, for example, tricked people into using a fake website that looked even better than the actual PayPal site. This is the exact tactic Trojans use, too: they’ll try to look as much like a different program as possible in order to gain your trust. These phishing scams are becoming more and more elaborate.
We advise you to always contact an official company’s customer support (via their official website) if you’re in doubt about a message you’ve received from them.
3. Hacked Wi-Fi networks
Wi-Fi networks are often created for nefarious purposes or hacked by malicious actors. A hacker may create their own “hotspot” with a similar name to the one you’re trying to log into, such as “McDonald’s Free Wi-Fi.” They may even be able to gain access to unprotected routers and, from there, steal the data of everyone else that is connected to it, too. That’s why it’s so important to stay safe on public networks by using a VPN.
4. Spoofed messages
Spoofed messages may look real to you but have actually been created by hackers who pretend to be someone you know. Also, there are spoof text messages where instead of the sender’s number, you get just the name of a service provider, for example, your bank’s.
Spoofed messages are also common in emails. For example, a hacker may send you an email from the company UPS, which within the email itself may be spelled U.P.S. Also, by closely inspecting the sender’s email address, you may see that it doesn’t include the expected @ups.com.
But what will happen to your device if you access software that contains a Trojan? Below we will discuss how exactly your computer is affected when it is infected by a Trojan virus.
How Does Trojan Malware Infect Your Computer?
Broadly, there are two ways in which Trojan malware can infect your computer once you download it. These two ways are at the source of two kinds of Trojans, which we’ll discuss below.
1. Dropper Trojan
A dropper trojan already has a malicious program embedded in it. Phishing emails can be used to deliver dropper Trojans through infected files you are tricked into downloading. Once the file is downloaded, your device will be infected with malware without needing to communicate with an external server.
2. Trojan Downloader
Another kind of Trojan virus is a downloader Trojan. The downloaded Trojan, originating from a phishing email, for example, does not contain malicious code. It may look like a “legitimate file,” which, once it is opened, the malware is automatically installed. This type of Trojan horse communicates with an online server to launch attacks or download infected files from the internet. Hence, an internet connection is necessary for a downloader Trojan to work, whereas a dropper Trojan does not require an active connection.
What Are the Different Kinds of Trojan Malware?
There are many different kinds of harmful actions Trojans can take. Based on the harm they cause, Trojan malware can be classified into different types. We’ve explained some of the most common types of Trojans below.
Please note that the classifications below are illustrative. Trojans can often perform more than one function. However, we have used their primary purpose or objective to categorize them.
Information-stealing Trojans
These trojans are primarily geared toward obtaining sensitive and personal user information. Based on the kind of information they collect, they can be broadly classified into:
- Infostealer Trojan: The main objective of this Trojan is to access sensitive data, including health records, financial information, and social security numbers. The information obtained by the infostealer trojan can be used to cause financial and mental distress to the target.
- Banking Trojan: These are a special kind of infostealer Trojans. Banking Trojans are geared specifically toward obtaining the victim’s financial information. Such Trojans are often downloaded from duplicate websites of leading banks.
- Keystroke Logger Trojan: Keystroke loggers relay the victim’s typing history to the hacker. They can then use this to identify the victim’s passwords and security phrases to breach their accounts.
Device access and exploit Trojans
The primary objective of these Trojan horse virus attacks is to infiltrate and control a device. Once infiltrated, the hacker can use the device for various purposes. We’ve classified device access and exploit trojans into the following categories based primarily on how they infect a device:
- RAT (Remote Access Trojan): RATs focus on providing the hacker with control of a device without it being in their possession. By gaining remote access, hackers can access files, execute commands and corrupt the device in different ways.
- Exploit Trojan: As the name suggests, the exploit trojan uses vulnerabilities in software to infiltrate the device. Hackers frequently target zero-day vulnerabilities to infect devices and gain control over them.
- Backdoor Trojan: Backdoor Trojans specialize in circumventing authorization protocols and firewalls to gain access to a device, usually to launch a remote attack. They are very hard to detect as they function silently in the background.
- Fake AV Trojan: These types of Trojans appear as antivirus software. Usually, a fake AV Trojan claims that there are security threats on your computer and offers to remove the threats in exchange for a fee. The threats don’t really exist, and in reality, the Trojan is trying to extort money from you.
Spam and malware Trojans
These Trojans are used to spread other kinds of malware onto a user’s device. They can also be used to target networks with bogus traffic and spam. There are broadly three kinds of spam and malware Trojans:
- DDoS (Distributed Denial of Service) Trojan: DDoS Trojans infect a device to launch denial-of-service attacks. Usually, the Trojan malware will infect multiple devices and connect them to a single command-and-control center. Once they receive the command, they simultaneously target a network and flood it with traffic, causing it to crash.
- Ransomware Trojan: This Trojan locks up files and programs on a user’s device using encryption. The files can be accessed only after a ransom is paid, usually with cryptocurrency. Ransomware Trojans can cause serious financial damage to individuals and organizations.
- Spam Trojan: The Trojan-infected device is used to send spam mail and links to others. These emails often contain links that prompt users to download software containing the Spam Trojan, fuelling its further spread.
Famous Trojan Malware Attacks
The best way to understand the damage that Trojans can cause is by studying some real-life examples. Some of the most famous Trojan attack cases are covered below:
| Trojan | Description |
|---|---|
| Storm Worm (2007) | Emails discussing the effects of the Kyrill windstorm in Europe helped spread this Trojan horse infection. When the mail attachment was opened, the malware installed malicious programs that allowed hackers to control devices remotely. The eventual goal appears to have been the inclusion of the infected device in a botnet. |
| ZeuS (late 2000s) | ZeuS remains one of the most notorious banking Trojans to date. It spreads via phishing emails or online ads. While its primary purpose is to steal the victim’s financial information, it could also be used to include the device in a botnet. By the time the FBI cracked down on the hackers behind ZeuS, they had reportedly pilfered more than $70 million. |
| CryptoLocker (2013) | The CryptoLocker ransomware attack contained infected ZIP files that were mainly distributed via email. On installation, the malware encrypted a user’s files and denied access until a ransom was paid using Bitcoin. |
| Emotet (2014) | Another banking Trojan, Emotet, is considered one of the most costly Trojan malware. The main vector of spread is phishing emails related to financial topics, such as invoice payments. The malware has evolved over time and now includes advanced stealth features and the ability to install other kinds of malware. |
| SolarWinds (2020) | SolarWinds sent shockwaves across cybersecurity circles due to its potential impact on US Government agencies. It used Orion, a program developed by software company SolarWinds, to infect computers across the security supply chain. The Trojan malware is believed to have been inserted in one of Orion’s updates that users downloaded. |
How Can You Tell if a Trojan Has Infected Your Device?
As we’ve mentioned previously, many Trojans operate silently in the background and can be difficult to detect. However, there are some telltale signs of a Trojan malware infection.
1. Slower performance
Trojans, such as DDoS and spam Trojans, run various processes and tasks using your device’s memory and processor. Resultantly, you may notice a slowdown in your device’s performance. A simple way to check which programs may be slowing down your device is through Task Manager.
By running Task Manager, you can also see how much of your processing power, RAM, storage, and network capacity these processes are using. To bring up Task Manager for Windows:
- Click on the Windows logo on your keyboard or in your taskbar (or press Ctrl + Alt + Delete).
- Type “Task Manager” and click on the app icon (or choose “Task Manager” from the window that appears)
- You will see the Task Manager window on your screen.
- Have a look at all the programs running in the background. See anything unusual? That might be the culprit.
The “Activity Monitor” on a Mac is like the Task Manager on Windows. If you own a Mac and want to explore how your system’s resources are being used, follow these steps:
- The tiny magnifying glass icon can be seen in the top right corner of your screen. Click on it.
- Type “Activity Monitor” and click on the first option that appears.
- Look for any applications that seem to be using a lot of system resources.
The CPU, RAM, energy usage, storage, and network load are just a few examples of the system resources that are presented by category on a Mac.
Remember, though, that if your computer suddenly slows down, it doesn’t necessarily mean that it has been infected by a Trojan.
2. Unfamiliar software and files
Trojan malware can find many ways to stay hidden within your system, making it challenging to detect. Hence, if you run Task Manager, you will not be able to locate these Trojan viruses.
If you are checking the applications that are running and don’t recognize one of them, then your first step should be to stop this application. Then you can do a quick Google search to find more information about that program.
Moreover, suspicious software may not include publisher details, and this can be an indication of a Trojan infection.
3. Odd pop-ups or error messages
A sudden increase in pop-ups on your device can be an indication of adware installed via a Trojan. Websites that offer content such as free movies or music will most likely contain Trojans. If, for example, a previously pop-up free website now seems to have many ads and pop-ups, this probably means its browser has been hijacked.
In this case, it is better to avoid using these sites or research them online. Having a good antivirus program installed to block any suspicious activity can also help protect you from such threats.
4. Your antivirus has been disabled
Some Trojans have the ability to download specific malware to your device, thereby bypassing your firewall or disabling your antivirus software. Hence, it is essential to check regularly if your antivirus is active.
If you are using an antivirus program like Bitdefender, as soon as you open the app, it will inform you whether it is active or not.
However, there are other ways to check this if you are using a computer. If your operating system is Windows, you can check if your antivirus is active by doing the following:
- Click on the Windows logo at the bottom left-hand corner of your computer screen.
- Type “Windows Security” into the taskbar box.
- Select this app from the menu that will appear in the top right.
- Click on the program named “Virus & Threat Protection.”
- You should be able to see if your antivirus is working and whether you need to do anything else to enhance your protection measures against malware.
If you are a proud user of a Mac, you can follow these steps to check on your antivirus app:
- Click on the icon with the nine small squares on the taskbar.
- All your apps will now be visible.
- If you know you have an antivirus program installed, search for it by name in the search bar or scroll through the list of apps to find it.
- Click on the antivirus app.
- Verify that it is active. Simply see if the small shield in the menu is green, for example, in the case of Bitdefender.
How to Remove a Trojan From Your Device
If you notice some of the symptoms described above on your device, you should immediately take action to identify and remove the Trojan from your device. You can do this by either using an antivirus scanner or manually. The steps involved for both are described below.
Removing a Trojan from your device using an antivirus scanner
There are several antivirus scanners on the market that detect and delete Trojans automatically. If you’re not familiar with identifying malware and removing it, we’d highly recommend sticking to a scanner. Follow the steps below to remove a Trojan from your device using an antivirus scanner:
- Sign up for a subscription with a top-rated antivirus scanner like Bitdefender. We recommend Bitdefender because it combines user-friendly features and malware protection with strong privacy practices.
- Download and install the antivirus app or software onto your device.
- Run a scan of your entire device to discover potential Trojans.
- If a Trojan is infecting your device, the scanner will identify it and suggest steps for removal or quarantine of the infected file. You should review and approve the removal.
- Schedule regular scans of your device to prevent any future Trojan infections. It’s usually possible to schedule scans using the antivirus program’s setting menu.
Manually deleting a Trojan from your device
If you prefer to try removing the Trojan manually, there is a series of steps you need to take:
- Disconnect your device from the internet or any network to which other devices are connected. This helps reduce the chance of Trojan malware infecting other connected devices or communicating with its command and control server.
- Identify the file(s) infected by Trojan malware. Look out for suspicious files and pay attention to error messages you get. Searching online for your particular error code can help you identify the file.
- Delete the suspected file. It’s important to be careful when deleting files, as you don’t want to accidentally delete an important system file. We recommend deleting the file after booting up in Safe Mode on your device.
- Reset your system to an earlier recovery date if symptoms of Trojan malware infection persist. If your system isn’t backed up, a clean wipe may be necessary.
Once you’ve removed the Trojan from your device, you can also take further steps to mitigate the potential harm that the infection may have caused. The most important step is to reset your passwords and set new ones that are complex and hard to crack. You can also enable two-factor authentication to prevent the hacker from gaining access to accounts for which they have log-in credentials.
How Can I Protect My Devices From Trojans?
As with other forms of malware, there are some things you can do to protect your computer and devices from Trojans. Here are the most important ones:
- Be wary of attachments: Never open an attachment or download a program unless you know exactly what it is. This is true for all kinds of malware, but Trojans are a special case because they require action on the part of the user to infect your computer.
- Do not open unfamiliar links: We encounter several links while browsing the internet. While they present an easy way to navigate the world wide web, they are also a potent source of infection. Be careful when opening links on unfamiliar web pages, and always check whether the website is HTTPS encrypted.
- Keep your software up to date: Cybercriminals often identify vulnerabilities in software programs and exploit them to install malware. Software manufacturers frequently release updates that address these vulnerabilities, so it is essential you download the updates when available.
- Use a good antivirus: As we mentioned above, an antivirus scanner is the most effective way to detect Trojan malware on your device and eliminate it before it creates a problem. Most modern antivirus scanners, like Bitdefender, also come with a built-in firewall that prevents files containing a Trojan virus from being downloaded in the first place.
Final Thoughts: How to Stay Safe From Trojans
Trojans are an incredibly varied kind of malware that can perform many malicious actions on your computer. These activities may include stealing your financial information, logging your keystrokes, or even turning your computer into a “zombie” controlled by cybercriminals.
By exercising basic security measures and using antivirus software, you can considerably decrease your risk of being infected by Trojans. We also recommend using a VPN (Virtual Private Network) to encrypt your online activity and improve your overall internet hygiene. NordVPN is our highest-rated VPN for 2023, as it has top-notch security and privacy features coupled with excellent speeds.
Be sure to also check out our other articles about staying safe online, such as:
- What Is a Remote Access Trojan? Remove and Prevent Rats
- What Is Spyware? How Do You Protect Your Devices?
- What Is Ransomware? Tips on How to Prevent and Remove It
Do you have a specific question about what Trojans are or how they can inflict serious harm on your device? Check out our FAQ down below.
A Trojan virus can steal your personal data, encrypt your files, and install other types of malware to your device. However, there are ways to protect yourself from Trojans. You can use antivirus software or manually delete a Trojan from your device.
Trojan viruses are a serious threat because they can pose as legitimate programs and trick the user into downloading them onto their device. From there they can wreak havoc quietly without the user noticing.
There are different ways to remove a Trojan virus. If you are lucky to know which type of software in your device contains the Trojan then you can just uninstall the program and delete it. But in the case of Trojans you need to be proactive and install a good antivirus program to pick up and block all Trojans trying to infect your device.
