Trojans: What Are They and How to Protect Against Them?

Janis von Bleichert
Last update
12. Sep 2023

Broadly speaking, malware is either easy or difficult to identify. The first type slows down your computer (or prevents it from turning on ) and/or opens unwanted pop-ups outside of your browser.

Other times, malware is trickier and secretly makes its way onto your system. Once there, it pops up to tell you that your digital defenses have been neutralized and that your sensitive data has been stolen, copied, or locked.

This second kind of malware has a name: A Trojan horse, or simply "Trojan". The name has roots in the Ancient Greek legend of how a wooden horse loaded with its enemies was brought inside Troy's gates. In this article, we'll show you what Trojans are, what kind of damage they can do, and how to avoid King Priam's mistake.

What Is a Trojan?

Trojans are a kind of malware that disguises itself as legitimate software to sneak onto systems and unleash damage. Freeware is one particularly popular vehicle that Trojans piggyback on, however, they can also find enter your system as (harmless-looking) email attachments.

How much damage a Trojan can cause depends almost entirely upon what sort of malware it smuggles onto your system. Just like in Homer's ancient tale, the Trojan (horse) itself is just the 'transport' for the real danger, which waits inside. Since there are many different kinds of Trojans, and new variants appear every day, we've summarized a few of the most important types for you below:

  • Banking Trojans/ Spyware
    These actively search for online banking information, hitting users in their bank accounts. Unlike extortion software or ransomware, banking Trojans try to rob you by misdirecting or rerouting transactions. The amount of damage they're capable of depends on how long it takes you to notice that something isn't right with your online banking or accounts.

  • Cryptotrojans
    Alternatively known as extortion Trojans, or most commonly as ransomware, these are the more aggressive and brazen sibling of spyware. Instead of secretly monitoring your activity, they encrypt folders or systems and demand payment for the decryption key. If you don't want to pay up, most ransomware displays a countdown timer showing how long you have until your files are permanently deleted.

    Never pay up, since as the old saying goes, "there's no honor among thieves."

  • Backdoor
    These compromise your system by opening it up to cybercriminals, who can then control and manipulate it for their own purposes. Most of the time, security mechanisms that protect you against malware will be disabled, and illegal activity will be performed without your knowledge.

  • Botnet
    A botnet isn't necessarily something bad. Any network of computers connected to one another that pool their resources to complete a task is a botnet. The problem arises when a botnet engages in illegal activity or uses a system without its user's knowledge, such as for DDoS attacks, or to send spam emails.

How Does a Trojan Get On My System?

The good news first: As tricky as Trojans are, they can't access your system unless you download a corrupted file that they're on. There are two main ways that malware gains access to systems:

  • Corrupted software downloads
    Trojans like to disguise themselves as harmless software or by piggybacking on legitimate software. For this reason, be careful which freeware you download, particularly from questionable sources. 'Free games', which often show as pop-up banners on websites, are a popular attack vector for Trojans.

  • Email attachments

    These are another favorite among cybercriminals to gain unauthorized access to a system. You've probably had a Nigerian prince try to send you millions (or billions) of dollars. However, cybercriminals now send legitimate-looking messages and pretend to be Google, PayPal, or other large companies. If you've downloaded an attachment from one of these, it's too late.

How Can I Protect Against Trojans?

Since Trojans can only access your system through data transfers (like downloads), patience and common sense are two of the best ways to defend against them.

Does the email you received from PayPal not include your name and/or contain an attachment? Or maybe the casino game on the website banner asks you to download and install a file after winning a few rounds? Think for a few moments, and when something seems fishy online, it probably is. Other steps you can take to enhance your protection against Trojans include:

  • Download software only from reputable sources
    It's always best to download software directly from its developer or official mirrors. Avoid free banner games, or other types of freeware that seem too good to be true. If a website looks suspicious, it probably is. Err on the side of caution and only download software from reputable sources.

  • Be careful when opening email attachments
    Before downloading an email attachment, always check the sender at least twice. A message from Amazon, eBay, or PayPal might look legitimate, however, hover your mouse over the sender's address: If you don't see an "" or "" ending, they didn't send the message.

    Another way to check an email is by entering its exact subject line in a search engine. If results note that it's a malware scam, you'll have your answer quick enough.

  • Regularly update your operating system, drivers, and software
    Malware and anti-malware are in a sort of Spy vs. Spy struggle with one another. On the anti-malware side (including software developers, like Microsoft), there is a constant effort to close the loopholes or exploits that malware developers uncover and exploit. Older operating systems or software are easy prey, so do yourself a favor and regularly update both to reduce your exposure.

  • Use antivirus software
    There is dedicated software that specifically protects against Trojans. With the right antivirus program, you can rest easy knowing that it is patrolling and monitoring your computer or laptop in the background. Apart from Trojans, these will also guard against many other types of malware and threats.

How to Remove a Trojan?

If you've already fallen victim to a Trojan, you'll need to download and install dedicated software to take back your system. Don't worry: Our step-by-step walkthrough shows you the way!


Trojans are tricky, relentless, and unforgiving malware carriers. They secretly leach onto your computer and wreak havoc long before users are any the wiser. To avoid them, be as careful online as you are in real life; don't open suspicious emails or attachments, and if something seems too good to be true, it most likely is.

As long as you pay attention to which files and software you download, as well as the websites you visit, there shouldn't be any issues. However, if a problem arises, you can rely on to help navigate you out of harm's way and win the 'Trojan War'.

Janis von Bleichert studied business informatics at the TU Munich and computer science at the TU Berlin, Germany. He has been self-employed since 2006 and is the founder of He writes about hosting, software and IT security.
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