What Is A Trojan?

A trojan is a cybersecurity term for a type of malware that disguises itself as something harmless like a legitimate application or document and tricks you into installing it.

Why Are Trojans So Dangerous?

Trojans are dangerous because they hide in plain sight. They rely on deception, posing as something safe while quietly slipping into your system. They often are buried in a download or innocent-looking email attachment, and once activated, they wreak havoc.

How Do Trojans Work?

While their exact behaviour can vary, most follow a familiar pattern built around trickery, silent installation, and stealthy execution. Here’s how the typical trojan attack plays out:

• 1

  Disguised And Delivered

  Attackers often hide malicious code in files that appear legitimate, like fake invoices, browser updates, or software installers. These are typically delivered through phishing emails, suspicious links, or compromised websites.

• 2

  User Takes The Bait

  Trojans rely on user interaction to activate. That might mean running a file you thought was safe, or following a prompt that looks like a routine update. That one click is all it takes, and the trojan is in.

• 3

  Trojan Installs Silently

  From there, the trojan installs in the background. It often sets itself to auto-run every time your device starts. You won’t get an error message, a warning, or any obvious signs that something’s wrong.

• 4

  Waits For A Trigger

  The trojan doesn’t always strike immediately, even after getting installed. It may lie dormant until triggered by a specific command like visiting a banking site or connecting to a network.

• 5

  Starts Causing Damage

  Once triggered, the trojan gets to work. Depending on its purpose, it might, log your keystrokes to steal passwords, give remote access to your device, download additional malware, or exfiltrate sensitive files.

• 6

  Post-Execution

  Once the trojan completes its main objective, it doesn’t always stop there. Depending on what it’s built to do, it might, delete itself to cover its tracks, stay active to continue stealing or spying, or return to dormancy and wait for its next command.

  Not every Trojan follows the exact same playbook. They all rely on deception and need you to install them. When they activate, how they behave, or how long they stick around, all depends on how they’re designed.

Why Is Trojan Horse Malware So Popular?

Attackers use trojans because they’re quiet, effective, and incredibly versatile. These are the most common motives behind trojan attacks;

Why Are They Referred To As Trojan Horses?

The name comes from the legendary Trojan Horse scam of ancient Greece. The Greeks built a massive wooden horse. Inside, soldiers quietly hid. They tricked the Trojans into dragging it into their city. Once night hit, the hidden army snuck out of the wooden horse and opened the gates for a full-scale invasion.

In cybersecurity, a Trojan works the same way in which it hides malicious code inside what appears to be a safe application. You think you’re installing trusted software, but behind the scenes, it’s already opening the door for attackers.

Types Of Trojan Malware

While trojans can deliver many forms of malware, some types are more commonly seen than others. Here's a breakdown of the most frequent ones attackers use;

Access And Control Trojans

These Trojans give attackers remote access or create hidden ways back into your systems.

• Remote Access Trojans (RATs): Let attackers take full control, like logging keystrokes, spying via webcams, and stealing files.
• Backdoor Trojans: Create secret pathways for attackers to slip in and out undetected, even after malware is removed.
• Rootkits: Help other malware stay hidden by burying deep in your system and masking their activity.

Data Theft Trojans

Built to steal credentials, files, or monitor activity without raising suspicion.

• Banker Trojans: Mimic bank alerts to trick users into handing over login credentials.
• Spyware Trojans: Capture keystrokes, screenshots, and track device activity silently.
• SMS Trojans: Send premium-rate texts or access SMS data for two-factor authentication bypass.

Delivery And Deployment Trojans

These act as the opening act by getting in quietly and bringing in the real damage.

• Downloader/Dropper Trojans: Look harmless at first but download other malware once inside.
• Exploit Trojans: Take advantage of known vulnerabilities to infect systems without needing user interaction.

Disruption And Extortion Trojans

Focused on creating chaos or holding systems hostage.

• Ransom Trojans: Encrypt files and demand payment to restore access.
• DDoS Trojans: Turn infected devices into bots used to flood and crash websites or networks.

Fake Utility Trojans

Disguised as helpful software but built for scams.

• Fake Antivirus Trojans (Scareware): Trick users with fake virus alerts and pressure them into paying for fake fixes.

Real World Examples

Zeus Trojan

First spotted in 2007, Zeus (aka Zbot) became one of the most successful banking trojans ever. It stole login credentials by logging keystrokes and scraping browser data, hitting millions of devices around the world.

It spread through phishing emails and malicious downloads, staying hidden while silently compromising everything from small businesses to government networks. When the source code leaked in 2011, it gave rise to countless variants, many still active today.

Zeus set the standard for stealthy credential theft. The original might be gone, but its legacy is still causing chaos.

CrypoLocker Trojan

CryptoLocker slammed Windows systems in 2013, spreading through phishing emails dressed up to look like legit messages from FedEx, UPS, and other trusted names. One click, and it was game over. Files across your device, network drives, and even cloud storage were instantly encrypted and locked tight.

Victims were hit with a Bitcoin ransom demand. Pay up or lose everything. The encryption was no joke and breaking it was nearly impossible without the key. By the time authorities shut it down, CryptoLocker had raked in over $27 million. A free decryption tool eventually surfaced, but by thenit was too late.

The campaign showed the world ransomware wasn’t just a threat, it was a business model.

How To Recognize A Trojan?

Trojans can be difficult to spot as the are designed to look innocent. However there are some typical signs that a trojan is raging war on your device;

• Unexpected System Behaviour - Your computer could start freezing, crashing, or rebooting for no reason.
• Sluggish Performance - Trojans often chew through CPU and memory in the background, slowing everything down, even when you’re not running anything heavy.
• New or Unknown Programs - You may notice apps or files you didn’t install. Trojans often drop extra payloads, spyware, keyloggers, or backdoors without your permission.
• Pop-Ups or Ads Out of Nowhere - Trojans love bundling in adware. If your screen’s lighting up with random ads or redirects, something’s hijacked your system.
• Disabled Security Tools – Your antivirus stops working or doesn’t update.

CanIPhish Tip:

If you’re seeing more than one of these signs, don’t ignore it. Run a full malware scan immediately. Trojans don’t go away on their own, they dig deeper the longer they’re left alone.

How To Protect Against Trojans

Guarding your systems from trojans requires a defense-in-depth mindset. Here are some common stratagies to protect against trojans:

• Install Antivirus Software - Installing antivirus software is the first step in protecting against trojans. It scans for threats in real time and blocks malware before it has a chance to cause any damage.
• Update Software Regularly - Outdated software is one of the most common ways cybercriminals break in. Hackers actively target known vulnerabilities, and patches exist specifically to close those gaps. Keeping your systems up to date gives attackers fewer opportunities to exploit you.
• Avoid Suspicious Downloads - Trojans love hiding in sketchy downloads. Skip the third-party sites and get your software straight from trusted sources like the official app store or the vendor’s website. Free software that looks too good to be true usually comes with strings attached.
• Unknown Links And Attachments - Phishing emails are the digital trojan horse, disguised as something helpful, but packed with trouble. Don’t click links or open attachments in emails you weren’t expecting. Even if it looks legit, think twice, it could be a spoofed message from a cybercriminal trying to bait you.
• Trusted Sources Only – Trojans thrive on fake software, updates, and websites. When it comes to downloading, always stick to official vendors, verified app stores, and well-known platforms.
• Train Your Team - Trojans don’t hack people. They trick them. One click on the wrong file or fake link is all it takes. Your team needs to know what to look for. Phishing emails, shady attachments, dodgy downloads, it’s all part of the playbook. If they can’t spot the bait, they’ll take it.
• Strong Passwords And MFA - Trojans are built to steal credentials. If your password’s weak, reused, or guessable, you’ve already handed them the keys. Use long, complex passwords and never recycle them across accounts. Add multi-factor authentication (MFA) and even if they grab your login, they’re still locked out.

How Should You Respond To A Trojan Attack?

If you’ve been hit with a Trojan, the goal is simple: contain it, clean it up, and lock things down. Here's how:

• 1

  Cut The Connection

  Immediately disconnect from the internet. This stops the trojan from spreading or communicating with its command center.

• 2

  Isolate And Scan

  Quarantine the affected device physically or logically. Then, run a full antivirus or anti-malware scan using up-to-date software. If you're at work, notify your security team straight away.

• 3

  Reboot And Remove

  Restart in Safe Mode to limit what loads at startup. This gives your security tools a better shot at cleaning things up. Remove or quarantine anything suspicious. If the damage is severe, consider a full reset.

• 4

  Reset Passwords

  From a clean device, change passwords for critical accounts, emails, banking, work systems, admin logins. Assume anything tied to the infected machine is compromised.

• 5

  Hunt For Hidden Threats

  Trojans often leave backdoors. Use tools like Autoruns or RootkitRevealer to detect and remove any lingering persistence mechanisms.

• 6

  Restore And Harden

  If possible, wipe and reinstall the system using a pre-infection backup. Avoid restoring anything saved after the attack. Next, patch your operating system, apps, and browsers. Finally, reinforce your security setup with multi-factor authentication, firewalls, and endpoint protection

Frequently Asked Questions

Are Trojans The Same As Viruses?

No, trojans and viruses are not the same. Viruses spread on their own because they are self-replicating. It spreads like digital mould from system to system or file to file without help. Trojans are a type of malware that tricks you into installing it. It doesn't spread on it's own. You’re the one that unknowingly gives it access. Either way, If your guard’s down, they both won’t hesitate to take over.

Can Antivirus Software Stop Trojans?

Yes, antivirus can help block Trojans, but it’s not foolproof. The better ones don’t just look for known malware, they also watch for suspicious activity that might hint something’s off. So even if a Trojan’s hiding in new clothes, there's still a chance it gets caught.

That said, you’re still the first line of defense. If you’re clicking shady links, opening random attachments, or turning off your protection, even the smartest antivirus won’t save you.

Can Trojans Infect Phones?

Absolutely. A smaller screen doesn’t mean smaller risk. Your phone is just as much a target as your computer. The same rules apply on your phone as on your computer. Stick to official app stores, be cautious with links, and keep your Operating System (OS) up to date.

Is Android More At Risk From Trojans Than iOS?

Yes, Androids have an open app ecosystem, meaning apps can be installed even if they’re not from the official Play store. This flexibility makes it much easier for malicious apps to slip through. It sounds fun to be able to customize your device with special features, but it comes with extra risk.

iPhones have stronger restrictions, but that doesn’t mean you're invinicible. If you install apps or tweaks from outside the App Store, you’re stripping away Apple’s built-in security protections, essentially tearing down the barriers that keep malware out. No matter your device, the moment you loosen security, you open the door to threats.