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An Introduction to Trojan Horse Malware

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By: Grimm

January 4, 2016

An Introduction to Trojan Horse Malware - Cybrary

There are different and distinct types of malware. In this post, we'll discuss Trojan Horse Malware. We'll cover what a Trojan Horse is, some of what they're capable of doing, how they're spread and what to do if you have one on your system.

According to Kaspersky Labs, six of the top ten web-based malicious programs of 2015 were Trojans. You can't miss the high-profile types of Trojan attacks in the news, which include Ransomeware.

Some believe that only Windows computers are susceptible to malware attacks. However, there have been instances of Trojans designed for OSX and even Linux. They're problematic for all users.

What is Trojan Horse Malware?

Trojan Horse Malware is an executable program that performs a malicious task while also doing something, or appearing to do something, benign. For example, in 2011 there was an OSX Trojan that imitated the Adobe Flash installer. That same year, another Trojan was hidden inside a PDF file that also targeted OSX.

In these examples, the malicious program is embedded into something that a user could potentially want and willingly downloads. But, unlike some other malware, Trojans do not self-replicate or reproduce by infecting other files.

What do Trojans do?

Trojans have a variety of abilities and purposes. The 2011 PDF file Trojan mentioned above attempted to install a backdoor in the OS to grant unauthorized access. From the Kaspersky Labs website, we find that Trojan Horse Malware performs actions including installing rootkits, installing backdoors, stealing/modifying data, locking a computer so it can't be accessed, and much, much more.

An Ounce of Prevention

One of the best ways to prevent infection from a Trojan attack is to download only programs and information from trusted sources. Keeping software up to date to patch vulnerabilities will also help to prevent infections. If a vulnerability a Trojan is designed to exploit has been fixed by a patch, the Trojan will not be able to exploit it. Antivirus software that's regularly updated can also help protect your system from Trojan attacks.

If You've Been Infected by a Trojan

There are several tools available for users who've been infected by a Trojan. Certain websites are designed to scan your computer for Trojan infections, though it's important to choose wisely - some websites claim to scan your computer, yet will install malware while doing so.

Several of the major antivirus companies have online tools to help with the removal of malware. Yet, the only 100% sure way according to some is to completely reinstall your operating system. In fact, in cases where Ransomeware has completely locked a system, reinstalling may be the only option.

It's important to know what Trojan Horse Malware is and how it spreads, to protect your systems form infection. Equally important is to know what tools are available to help mitigate exposure to infection and what to do if you suspect your system has been compromised.


Cluley, Graham, “Mac OS X Trojan hides behind malicious PDF disguise”, Naked Security, Sophos, 23 SEP 2011, 31 Dec 2015,

Kaspersky Lab, “What is a Trojan Virus?” Kaspersky Lab, 27 Dec 2015,

Kaspersky Lab, “Avoiding a Trojan Virus: Keeping the Gates Closed” Kaspersky Lab, 27 Dec 2015,

Kaspersky Lab, “Kaspersky Security Bulletin 2015”, Kaspersky Lab, 30 Dec 2015

Kessler, Topher, “Another OS X Trojan imitates Adobe Flash Installer” C|Net, 26 Sep 2011, 30 Dec 2015,

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