In-depth

What is a Trojan?

The malicious malware lurks behind legitimate software to invade your computer

Toy horse on a digital screen to symbolise the attack of the Trojan virus

What was once the name for a wooden horse that was used to sneak Greek soldiers inside the walls of Troy is now a term that puts IT professionals on edge. A Trojan, often referred to as a Trojan horse, is a form of malware disguised as legitimate software that either causes damage to a user's device or enables external access to it.

As their namesake suggests, Trojans prefer to remain undetected on a user's machine, slowly gathering information about it before performing malicious functions. Once inside, it can copy info to send back to its creator, block access to data, and even drain the machine of resources.

There are a number of Trojan classifications and each one can perform different malicious tasks on your computer, such as embedding a backdoor or injecting rootkits which conceal certain objects or activities in your system. There are Trojans that attempt to take financial information and even those that attack with DDoS software.

In 2019, an internationally coordinated effort from law enforcement agencies sized a website selling Trojan tools thought to be responsible for infecting thousands of computers. A larger percentage of these were remote access Trojans (RATs) that were sold for as little as $25.

Once a trojan has made its way onto a machine it's often too late to prevent malicious functions from initiating, making it one of the most effective tools for hackers.

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.

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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