What is a Trojan Virus? How to Prevent and Remove it

When Virgil wrote his epic poem The Aeneid between 29 and 19 BC, little did he know that his work would resonate through the ages. Among its most enduring tales is that of the Trojan horse: a cunning ploy by the Greek army to infiltrate the walled city of Troy through deception. Instead of directly attacking the city’s walls, they feigned retreat, leaving behind a giant wooden horse as a supposed gesture of surrender. Fooled by this apparent gift, the Trojans unwittingly wheeled the horse, transporting the hidden army, inside their walls, thereby sealing their own fate.

Fast-forward over 2,000 years, and Trojan Horse Viruses, often referred to as “Trojans,” echo this ancient strategy in the cyber world. Only now, the perpetrators – cybercriminals – use social engineering tactics to deceive unsuspecting users into running seemingly harmless programmes with hidden malicious intent. Unlike ancient warriors wielding swords and shields, these modern adversaries aim not to ransack cities but to compromise, steal from, disrupt or otherwise damage your network and systems.

What is a Trojan Horse Virus?

A Trojan virus is a type of malicious software (malware) that disguises itself as a legitimate programme or file to trick users into downloading and installing it on their computers or devices. Once inside your networks or systems, they can perform destructive actions before you even know they are there. Some will lay dormant on your computer, waiting for further instructions from the attacker, while others begin various types of malicious activity straightaway. This could include:

• Data Theft: Trojans can steal your most personal information such as login credentials, banking details and data stored on the infected device.
• System Damage: Some Trojan viruses are designed to corrupt files, modify system settings or delete crucial data on the infected computer. This can lead to system instability, loss of important files and can even render the computer unusable.
• Remote Access: Certain Trojans create a backdoor, giving remote hackers unauthorised access to the infected computer. This access can be used to install additional malware, steal confidential information, monitor user activities or turn the infected device into part of a botnet – a network of compromised devices controlled by attackers to conduct large-scale cyber attacks.
• Spying and Monitoring: Trojan viruses can monitor user activity, record keystrokes and capture screenshots, providing attackers with valuable information about the victim’s online behaviour and activities.
• Financial Fraud: Some Trojans are specifically designed to intercept online banking transactions, redirect payments or steal payment card details, leading to unauthorised financial transactions.

How Trojan Viruses Infect Computers

Trojans have many faces, meaning they can disguise themselves as something legitimate and desirable, such as free music, browser advertisements, apps – the list is endless. User behaviour plays a big part in Trojan infections, including:

• Downloading Free Software: Users may download free or pirated software from untrusted sources. These downloads often contain Trojans bundled with the legitimate-looking software, tricking them into installing malware on their devices.
• Clicking on Ads and Pop-ups: Internet advertisements, especially pop-ups, can be used to distribute Trojans. Users who click on these ads might unknowingly download and install a Trojan virus on their computer.
• Opening Email Attachments: Cybercriminals send phishing emails appearing to be from trusted sources, enticing recipients to download attachments or click links containing Trojan malware. Users who open attachments from unknown or suspicious sources risk infecting their devices with malware.
• Visiting Compromised Websites: Some websites are specifically designed to distribute Trojans. Simply visiting these sites or downloading content from them can result in an infection on your computer.
• Social Engineering: Attackers use social engineering tactics to trick users into downloading and installing malicious software voluntarily. This could include fake alerts about viruses or computer problems, prompting users to download a “fix” that is actually a Trojan.

How Trojans Impact Mobile Devices

Laptops and desktop computers are not the only devices at risk from Trojan viruses. Mobile devices, such as smartphones and tablets, are also vulnerable to Trojan attacks. These Trojans typically masquerade as legitimate apps on unofficial and pirate markets, enticing you to download them before infecting your device with malicious software, such as ads and keyloggers.

Here are some examples of Trojans that target mobile devices:

• Switcher Trojans: These redirect traffic on Wi-Fi-connected devices, allowing attackers to commit cybercrimes using the compromised network.
• SMS or Dialler Trojans: These infect mobile devices and can send or intercept text messages without your knowledge, potentially leading to unauthorised charges or data breaches.
• Banking Trojans: These are designed to steal financial information by overlaying fake login screens on top of legitimate banking apps, tricking you into entering your credentials.
• Ransomware Trojans: These lock you out of your device or encrypt your data, demanding a ransom to restore access.

How to Prevent a Trojan Virus

A comprehensive digital security strategy should combine proactive security measures with end-user vigilance. Since Trojans rely on deceiving users into letting them into a device, awareness and caution are the first line of defence against Trojan viruses and other threats.

Here are some top technical and behavioural tips to help prevent different types of Trojan attacks:

• Install and Update Anti-Malware Software: Ensure you have robust anti-malware software installed. Keep it updated so it can recognise, isolate and remove malicious code quickly and effectively.
• Keep Operating Systems Updated: Set your computer or device to update automatically, ensuring you have the latest security patches and updates.
• Update Applications Regularly: Regularly update all your applications to patch any security vulnerabilities that could be exploited by Trojans.
• Adjust Windows Settings: Change default settings to make file extensions visible, helping you identify suspicious files more easily.
• Use Firewalls: Operate behind a firewall whenever possible to provide an additional layer of security.
• Ignore Pop-Up Ads: Avoid clicking on pop-up ads, which can be a common source of Trojan infections.
• Be Cautious with Email Attachments: Never open or download attachments from unknown sources or emails that look suspicious.
• Use Strong, Unique Passwords: Employ complex and unique passwords or passphrases for different services and websites.
• Backup Files Regularly: Regularly backup important files to ensure they can be easily recovered in case of an infection.
• Download from Trusted Sources: Only install or download programmes from verified, trustworthy sources.

By understanding these behaviours and being cautious about your online actions, you can create a secure digital environment, minimising the risk of falling victim to Trojan attacks.

How to Detect a Trojan

A Trojan virus can infiltrate your device and operate undetected for months without you knowing, making them particularly insidious. However, there are several signs you can watch out for that may indicate a Trojan infection. Detecting these symptoms early can help you minimise the damage and remove the malicious software more effectively.

• Poor Device Performance: Is your device running slowly or crashing frequently?
• Strange Device Behaviour: Are programmes you didn’t initiate running on your device, or are other unexplained processes being executed?
• Pop-Up and Spam Interruptions: Have you noticed an increase in browser pop-ups or email spam?
• Unusual Network Activity: Is there a spike in network traffic or unusual data usage?
• Changed Settings: Have your computer settings changed without your intervention?

The best way to recognise a Trojan is to search your device using a dedicated Trojan scanner or malware-removal software. These tools are designed to identify and isolate various types of malicious files, providing a thorough analysis of your system. Regular security audits and continuous monitoring of your device’s performance and network activity can also help detect unusual behaviour indicative of a Trojan infection and other malware.

How to Remove a Trojan From Your Computer

Once a Trojan infects your device, it is crucial to clean it up and restore the system to its desired state as soon as possible. Using an effective automated anti-malware tool to perform a full system scan is the most reliable method.

However, you can also remove a Trojan virus manually by following these steps:

• Stop System Restore: Ensure you disable system restore to prevent the reinstallation of the malicious files you delete.
• Restart Your Device: Boot your device in “Safe Mode” to limit the number of active programmes and make it easier to find and remove the Trojan.
• Remove Infected Programmes: Uninstall all programmes affected by the Trojan.
• Delete Extensions: Erase all related programme files by removing them from the system folder.
• Restart in Normal Mode: After cleaning, restart your device in “Normal Mode” to check if the virus has been completely removed.

Don’t make the same mistake the Trojans did all those years ago by letting your enemy in through the front door. Cybercriminals are masters at the art of deception, so stay one step ahead of them by taking proactive measures to prevent Trojan attacks on your business.

Discover our Cyber Security services to learn how we can help protect your business.