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In-depth

What is a Trojan?

The malicious malware lurks behind legitimate software to invade your computer

Not everything is what it seems in computing; sometimes a simple download can actually be malware in disguise - a hacking method known as 'Trojan'.

This is the digital version of the famous tactic the Greek army used to infiltrate the city of Troy. The payload for the modern equivalent is your data, be it personal or financial, which might be found in your hard drive. 

Once it is downloaded, a Trojan virus will lay low, simply gathering information for its creator - often people have no idea their machine is compromised. It has been known to block access to data and even drain resources while hiding in a victims machine. 

Trojan's are widely available and relatively inexpensive, often used in DDoS attacks and also as vehicles for other viruses, such as ransomware. A 2019 NCA investigation found that remote access Trojans - known as 'RATs' - were available for as little as $25 (£19), which is part of the reason they're so popular. 

Aside from price and availability, Trojans are also seen as some of the most effective tools available for hacking, especially considering that in most cases, victims only realise one is on their machine at the last minute. 

Types of Trojan

What is important to remember is that the term “Trojan” is actually just an umbrella term for a wide variety of malware types, from RATs to cryptocurrency miners. In fact, Trojans are usually named after the way they behave once they gain access to a system.

Backdoor Trojans, sometimes referred to as remote access Trojans (RATs), are built with the intention to allow cyber criminals to grasp full control over a system. They achieve this by creating a so-called backdoor that lets them come and go as they please for as long as the Trojan goes undetected, and can be used for an array of illegal activities, from spying on users to implementing larger cyber attacks.

Download Trojans, as their name suggests, are capable of downloading other malicious programmes once they gain access to a system. The most common tools are keyloggers, which harvest any usernames and passwords entered into the system, or cryptocurrency miners, which take advantage of a system’s processing power in order to subtly mine for Bitcoin as well as other digital tokens.

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Banking Trojans, otherwise known as 'Trojan bankers', focus primarily on financial gain. They are able to conceal themselves within a system, waiting for the moment when the user decides to access a financial service such as an online bank account. They then intercept this traffic and redirect their victim to a fraudulent website which usually contains data capture forms used to steal the victim’s information.

Banking Trojans have enjoyed considerable success in the past, with some famous examples including Zeus, Dridex, and Kronos. However, with today's heightened security measures as well as proactive efforts to prevent this style of attacks, banking Trojans aren't as common as they used to be.

Hands of man holding a smartphone and using a laptop computer to make an online purchase

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How to protect against Trojans

While Trojans can cause significant damage if loaded on someone's system, there are ways to prevent malware from causing problems.

Simple steps such as avoiding unsafe websites and keeping accounts safe with secure passwords and firewalls can help prevent malware attacks. Updating a device's operating system as soon as possible will also help prevent Trojans from causing damage as malware tends to exploit the problems in outdated software.

It's also advisable to back up your files regularly, as if a Trojan infects your computer, this will help you to easily restore your data.

However, perhaps the most effective way of preventing this kind of malware attack is by installing anti-malware software on devices and running diagnostic scans with this software periodically.

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