What Is a Trojan Horse Virus? The Ultimate Guide to Types, Risks, and Protection

A Trojan Horse computer virus, commonly known as a Trojan,  is a type of harmful software (malware) that tricks you into downloading it. Unlike other types of malware or viruses that spread by themselves, Trojans need you to download or open them.

Once inside your device, they can cause serious damage. They can steal your personal information, give hackers control of your device, or install other harmful software.

Key Takeaways

• Trojans are different from viruses because they don’t spread on their own. They usually look like harmless files, such as games or email attachments, and require you to open them to infect your system.
• After a Trojan infects your device, it can stay hidden in the background, making it difficult to detect or remove. Some even turn off your antivirus software, which allows them to keep doing damage for a long time without being noticed.
• To prevent getting a Trojan, it’s important to be careful. Avoid downloading files from unfamiliar or untrustworthy websites, don’t open attachments from suspicious emails, and always update your software to make sure you’re protected from the latest threats.

The Origin of the Trojan Horse Virus

The Trojan Horse meaning comes from an old story where the Greeks tricked the Trojans with a wooden horse. The Greeks used a large wooden horse to trick the Trojans into letting it into their city. Soldiers were hiding inside the horse. Once the Trojans brought it inside, the Greeks came out of the horse at night and attacked. In the world of computers, a Trojan works in a similar way. It hides inside something that looks safe, like a game, a free program, or even an email attachment. Once you open it, the Trojan can do its job: infect your computer and start causing harm. 

Unlike viruses, which can spread by themselves, Trojans need you to open or run them. Experts reported that over 1 billion malware programs exist, with Trojans making up about 58% of all detected threats. In 2024, antivirus systems detected an average of 467,000 malicious files every day, with Trojan detections increasing by 33% compared to the previous year.

Key Features of a Trojan Virus

• Deceptive Nature: A Trojan virus often looks like a harmless file, such as a free game, software update, or document. It tricks you into opening it, and that’s when it installs itself on your computer.
• User Installation: Unlike other malware that spreads automatically, Trojan Horse malware relies on you to download or run them. You have to help them get onto your system by opening the file or program.
• Malicious Actions: Once activated, a Trojan can do many harmful things. It might steal your passwords, install more malware, or give hackers remote control of your device.

How Do Trojans Work?

Trojans are dangerous because they trick you into letting them into your device. Here’s how they usually work:

1. Delivery

Trojans are often delivered through emails, fake software updates, or websites that trick you into downloading them. You might get an email with an attachment that looks like a document or image you need. Once you open it, the Trojan virus is installed without you knowing.

Trojans can also hide in free programs that you might download from suspicious websites. If you download cracked software (illegal copies of programs) or anything from untrustworthy sources, you may accidentally download a Trojan along with it.

2. Execution

Once the Trojan file is opened, it starts running on your computer. Depending on the type of Trojan, it may start doing different harmful things. Some Trojans steal information like your passwords or credit card details. Others might install more malware on your computer, or even take control of your device.

3. Persistence

Some Trojans try to stay hidden on your device. They might change your system settings or disable your antivirus software so that they can continue running without being noticed. This way, they can cause damage for a long time, and you might not even realize they are there.

4. Command and Control

Some Trojans establish a connection with an external server that the hackers control. This allows the attackers to send commands to your computer. They can do things like steal more data, install more malware, or control your device remotely. This is why Trojans are so dangerous; they give hackers easy access to your personal information and devices.

Types of Trojan Malware

Trojans come in many different types. Each one does something different, but they all use the same trick: they disguise themselves as something safe. Here are some of the most common types:

1. Backdoor Trojan

A Backdoor Trojan creates a hidden entry point into your computer. Once it’s installed, hackers can use it to access your computer anytime they want. This can be used to steal data, install more malware, or control your computer remotely.

2. Banker Trojan

Banker Trojans are designed to steal your financial information, especially from online banking. They trick you into visiting fake banking websites or steal your login details. Once they have access to your bank accounts, hackers can make unauthorized transfers or purchases.

3. Downloader Trojan

A Downloader Trojan doesn’t do much on its own. Its job is to download other types of malware onto your system. This could be more Trojans, spyware, or ransomware. Downloader Trojans often install even more dangerous threats.

4. Spy Trojan

Spy Trojans secretly monitor everything you do on your computer. They can record what you type on your keyboard (called keylogging), take screenshots, or track your online activities. Hackers can use this information to steal your personal details, like passwords or credit card numbers.

5. Rootkit Trojan

Rootkits are used to hide malicious programs from your security software. They allow hackers to stay on your computer for a long time without being detected. Rootkits can also prevent your antivirus from finding other malware.

6. Fake Antivirus Trojan

This Trojan pretends to be an antivirus program. It tries to trick you into thinking your computer is infected with a virus and asks you to pay for a “full version” to fix it. But instead of helping, it steals your money or installs more harmful software.

7. DDoS Trojan

A DDoS Trojan turns your computer into a part of a botnet (a network of infected devices). Hackers can use your device to send huge amounts of traffic to websites, causing them to crash. These kinds of attacks are often used to take down websites or disrupt services.

8. Ransom Trojan

Ransom Trojans are very dangerous. They lock your files, like photos, documents, or even your system, and demand a ransom to unlock them. If you don’t pay, you might never get your files back. This kind of Trojan is often used by criminals who want to make money from your misfortune.

9. Remote Access Trojan (RAT)

RATs give hackers remote control over your computer. With this access, they can do anything: steal your data, install more malware, or even use your computer to attack other devices. RATs are often used in espionage or to steal sensitive information.

10. SMS Trojan

SMS Trojans infect mobile phones. They can send expensive text messages to premium-rate numbers without your knowledge. You end up paying for these messages, and the hackers make money off your phone bill.

11. Trojan-Spy

This Trojan spies on your activities. It can log what you type, take screenshots, and track your online movements. It is used to gather information like passwords, credit card details, and private messages.

12. Trojan Game-thief

Trojan Game-thiefs target online gamers. They steal login credentials for gaming accounts, including usernames, passwords, and even payment information.

How to Recognize a Trojan Virus

Here are some signs that your computer might be infected:

• Slow Computer: If your computer suddenly starts running much slower than usual, it could be infected with a Trojan PC virus.
• Pop-up Ads: Unexpected pop-ups or ads, even when you’re not browsing the internet, might be a sign of a Trojan infection.
• Settings Changes: If your computer’s settings change on their own, like your homepage or default apps, it could mean a Trojan has taken control.
• Disabled Antivirus Software: Trojans often disable antivirus programs to avoid detection. If your antivirus stops working without explanation, a Trojan might be the cause.
• Unfamiliar Programs: If you see programs or files you didn’t install, they might have been added by a Trojan.

How to Protect Yourself from Trojan Viruses

There are several steps you can take to protect yourself and your devices from Trojans, ensuring computer virus prevention:

Use Antivirus Software

Make sure you have antivirus software installed and running. It will scan your computer for Trojans and other threats and remove them before they can do any damage. 

Be Careful with Email Attachments

Only open email attachments from people you trust. Even then, be cautious, as Trojans can disguise themselves in emails that appear to come from trusted sources.

Avoid Suspicious Websites

Never download software from suspicious or untrustworthy websites. Stick to well-known websites and official app stores to avoid downloading a computer Trojan Horse virus along with free programs.

Keep Your Software Updated

Always update your operating system, antivirus software, and apps to the latest versions. Updates often include important security patches that protect your device from Trojans and other threats.

Use Strong Passwords

Use strong, unique passwords for your accounts. If you have trouble remembering them, consider using a password manager. This will help protect your accounts from being hijacked by a Trojan.

Backup Your Files

Make sure you regularly back up your important files to an external drive or cloud storage. This way, if a Trojan locks your files, you can easily restore them.

Enable Two-Factor Authentication (2FA)

For sensitive accounts like online banking, use two-factor authentication. This adds an extra layer of protection even if your password is stolen by a Trojan.

What to Do If You Get Infected by a Trojan Virus

If you suspect your computer has been infected by a Trojan, follow these steps:

1. Disconnect from the Internet: This stops the Trojan from communicating with the hackers’ server and prevents it from spreading.
2. Run a Full Antivirus Scan: Use your antivirus software to scan your computer and remove any threats.
3. Restore from Backup: If your files are damaged or locked, restore them from a clean backup.
4. Change Your Passwords: Change passwords for important accounts, especially if you think they’ve been stolen.
5. Contact Your Bank: If you think your banking information has been compromised, inform your bank right away.

Final Thoughts

Trojans are harmful malware that rely on tricking you into opening or downloading them. Once a Trojan is inside your device, it can steal your personal information, damage files, or give hackers control. To protect yourself, always use antivirus software, be careful with email attachments and websites, and keep your software updated.

If you think you’ve been infected, run an antivirus scan, change your passwords, and contact your bank if necessary. Staying alert and following these steps can help keep your devices safe.

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