What is a trojan horse virus and how does it work?

The meaning of ‘trojan horse’

Think back to your Greek history for a second, and you might recall a famous story about the Greeks, who were at war with the Trojans, offering their enemies a gift of a giant wooden horse. The Trojans, suspecting nothing, gladly accepted the gift and wheeled it inside their city walls. This is exactly what the Greeks wanted because a cadre of Greek soldiers were hiding inside the giant wooden horse. Under cover of night, they snuck out and took over the city of Troy from the inside out.

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This legendary tale is a perfect touchstone for sneaky behavior that starts out seemingly innocent enough, perhaps even with the promise that it will be helpful or good for you. And this is where the Trojan horse virus gets its name—and you can probably guess that these trojan viruses, which are a type of malware, get inside your computer through otherwise seemingly safe messages or pieces of software. Sometimes only referred to as a “trojan,” there’s debate about whether this bit of malicious code is a true virus, but the “trojan” part of the name makes their inspiration clear, if misleading, since the Greeks concocted the whole horse scheme.

But the analogy doesn’t end there. Remember, the Greeks managed to convince the Trojans that the war was over and that the horse was a peace offering of sorts. In the same way, the trojan horse virus succeeds by making you think you want whatever is in the email attachment or pop-up ad that you’ve clicked on is safe. Sometimes, there’s an obvious invitation to open the message, which can be a social engineering tactic that hackers use to make you more likely to take their bait.

And much like the Greeks lying in wait inside the belly of the horse, this little bit of code could take months to be triggered into action. It may spring to life if you visit a certain website or perform a series of everyday computer maneuvers. Then, it can capture your information and use it to take over your bank accounts and profiles, spreading cyber destruction everywhere. There are trojans that can steal your passwords by monitoring keystrokes, lock files and set up ransom demands, use your computer as a ground zero for more cyberattacks and even hijack your instant messages and texts. Truly terrifying.

So you’ve opened a trojan horse virus—now what?

First of all, no matter what’s happening on your computer, don’t feel too terrible. Yes, you should practice good cyber hygiene and be careful opening attachments, especially from people you don’t know, and downloading unauthorized software. But also, remember that trojans are successful because you don’t know they’re there. Hackers can put a lot of time and effort into making the perfect vehicle for their trojan, so something like a bank email might look very legitimate with almost no tell-tale signs of fakery. And, because a trojan can take a while to become obvious, their insidious beauty is that you probably won’t remember or connect clicking on that ever-so-slightly off, in-game ad three months ago to the network chaos happening now.

How to save yourself from a trojan horse virus

But that said, if the city of Troy had asked a few more questions before wheeling the horse inside their gates, they could have saved themselves their fate. For our modern age, here’s some preventive tips to keep those sneaky Trojan horse viruses from invading your network.

• Watch those clicks and downloads of software. In a workplace, trust only the IT-approved sources for extensions and programs. In your personal life, try to use manufacturer websites for things like printers, drivers, and downloads.
• Check the email addresses of your attachments thoroughly. While the body of the email might look fine, hackers can succeed in sneaking by your defenses with things like slight misspellings of last names or different domain endings for websites. And if someone hasn’t emailed you before, be extra cautious in verifying their legitimacy.
• Practice good password management. We all know it can be a pain to remember multiple, complex passwords, but it’s far more painful to realize a trojan wriggled its way in through your weak spots. Passwords are a notorious point of vulnerability, so shore those up while you can, or get a well-projected password manager.
• Constant vigilance. Keep your virus scanners and malware removal software updated, and pay attention to your important assets. It’s possible there will be only subtle signs of the attack, like decreased computer performance or some unusual activity within the machine or the affected accounts, so it helps to prevent anything from taking hold or being able to stop an attack from spiraling too far.
• Always back up your device. If the worst happens and your defenses are breached, it’s a great plan to have been regularly backing up your system and data all along. That way you can restore, rebuild, and start over without too much damage. So, if this is news to you, start backing up your device now!

Trojan horse viruses are a very common hacker tactic in part because of how they work. But remember that the story of Troy and their wooden frenemy didn’t just spawn the concept of “Trojan horse” but also became an idiom for when things just seem a little too good to be true, or when there might be a hidden catch: Beware of Greeks bearing gifts. Explore more digital privacy and safety tips to avoid trojan horse viruses and more.