Is Your Computer Infected by a Trojan Horse? Signs & Fixes

A trojan horse is a type of malware that can infect any computer. Trojans find their way onto computers by hiding in software downloads, making them easy to (unintentionally) install. You can also get a trojan horse by visiting an insecure or malicious website. Once a trojan horse is installed on your computer, it can spy on you, steal your personal information, and/or create backdoors that allow other hackers to do the same. In this article, we asked tech and cybersecurity experts for tips on identifying common signs of a trojan horse virus and how to check for and remove trojans if found. We'll also cover how to prevent trojan horse infections in the future.

Trojan Horse Viruses: What to Know

A trojan is malware that tricks you into installing it by hiding in legitimate-looking software. A trojan horse infection can expose your personal data and/or allow a hacker to access your computer remotely. Some signs of a trojan: Sudden slowness, apps you don't recognize, pop-ups, and browser redirects.

Section 1 of 4:

What is a trojan horse virus?

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According to tech strategist Dan Rubianes, a trojan horse virus is an attack vector that you download on your system unsuspectingly, which exposes your system to remote access.^{[1]
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Dan Rubianes
Tech Strategist

Expert Interview} Trojan horse viruses usually appear to have some useful function, like speeding up your computer or giving you an advantage in a game, but they secretly contain some hidden element that allows an outside party to hack your computer.^{[2]
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Section 2 of 4:

Signs of a Trojan Horse Infection

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Your computer is running more slowly than usual. Trojans run software in the background that can use a lot of precious computing power. A "zombifying" trojan can even make it impossible for you to use your computer at all while the hacker is using it to attack a network.^{[3]
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You find unknown programs and apps. Are you seeing programs that you don't recognize, or are programs opening automatically that weren't before? Trojans install software on your computer that can be used to harvest your information or use your computer to attack others. You may not see these programs in your Start menu or Apps folder, but technology specialist Benjamin Phipps recommends also checking to see which apps and services are running in the background.^{[4]
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Brandon Phipps
Technology Specialist

Expert Interview}
- Cybersecurity expert Michael Thompson-Brown says you can check for background apps on Windows in Task Manager.^{[5]
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  Michael Thompson-Brown
  Cybersecurity Expert
  
  Expert Interview} To do this, just press Ctrl+⇧ Shift+Esc and look at the "Background processes" section.
- On Mac, you can check for unknown processes and programs in the built-in Activity Monitor app.
Trojans may install programs that cause pop-up windows to appear on the screen, sometimes asking for login or banking information. If you see a pop-up asking you for personal information, don't enter that information unless you specifically visited the website or opened the app first.^{[6]
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Your web browser is redirecting you to strange websites. If opening a new browser window or tab takes you to a strange website instead of your typical homepage, or going to a specific website now redirects you to some completely different website, your computer could be infected.^{[7]
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Section 3 of 4:

Checking For and Removing a Trojan Horse

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Install and/or update your antivirus software. Both Windows and macOS come with built-in security software designed to keep you safe from trojan horses and other threats. However, if your computer and antivirus software are not up to date, newer trojans may creep through.
- If you're using Windows 10 or 11, Microsoft Defender is always running in the background, doing frequent scans for trojan horses and other threats.^{[8]
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  Microsoft Support
  Technical support and product information from Microsoft.
  
  Go to source} To make sure it's up to date, open the Start menu, type update, and click Check for updates in the search results. Install any updates that are found.
  - Computer repair technician Spike Baron also recommends installing additional malware scanning programs like ADW Cleaner or Malwarebytes. "Between those two and Microsoft Defender, you can usually take out 99% of all viruses," he says.^{[9]
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    Spike Baron
    Computer Repair Technician
    
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- If you have a Mac, virus and malware protection is built into your computer already.^{[10]
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  Research source} Apple recommends keeping your system up to date to ensure the best protection. Click the Apple menu, select System Settings, click General, then click Software Update. Click Update Now if any updates are found.^{[11]
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Scan your computer. Any reputable antivirus/antimalware software can check your computer thoroughly for trojan horses. If your software detects a trojan horse, it will let you know and then help you remove it from your computer.
- Microsoft Defender is great at tracking down and removing most threats on its own, but for a deeper scan, you can run an offline scan. In the Windows search bar, type virus, click Virus & threat protection in the search results, and then click Scan Options. Select Microsoft Defender Offline Scan and click Scan Now.
- Although you have antivirus protection, you can't run a scan on a Mac without installing non-Apple antivirus/antimalware software. One of the most well-known available is Malwarebytes for Mac, and you can use it to scan your Mac for free. Download Malwarebytes from malwarebytes.com/mac-download, and then double-click the downloaded file to install the software. Once installed, open Malwarebytes and click Scan Now to start the scan.
- There are many other antimalware programs you can use on both Windows and macOS. Malwarebytes, Avast, and AVG are all available for both operating systems, and they all have free scanning options. Each of these programs also offers you the option to pay for an upgrade that will always run in the background so it can catch trojan horses and other malware in real-time.

Section 4 of 4:

Avoiding Trojan Horse Infections

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Protect yourself from trojan horses in the future. Whether your antivirus scanner found a trojan horse or not, you'll still want to do everything you can to make sure you stay protected from threats in the future.
- Keep all of your software up to date. When Windows or macOS prompts you to update to the latest version of the operating system, do it as soon as possible. While these update notices don't always pop up at the most convenient times, they are timely—updates usually contain security updates that fix issues that hackers can exploit. The longer you wait, the more vulnerable you are to attack.
- Don't install apps from sources you don't know and trust. Although it's not fail-proof, you'll have a better chance of avoiding trojan horses if you stick to installing software through the App Store app on your Mac or the Microsoft Store app on your PC.
- Be careful opening email attachments. Don't open attachments in email messages unless you're expecting the attachment. Trojan horses may infect your computer through a program file sent by someone else—even if the email message is from someone you trust, there's a chance a virus infected their computer and is now trying to install trojan horses on other people's computers.
- Avoid visiting risky websites. If your browser warns you that your connection is not secure, or you're being inundated with pop-ups or fake virus notices (these can look convincing!), close your browser tab, open a new one, and browse to a different website.

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What's the best anti-virus program?

Michael Thompson-Brown
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Michael Thompson-Brown is a Cybersecurity Expert based in Portland, Maine. He is the owner and founder of PCRescue!, a company that provides cybersecurity and data management solutions to small businesses and individuals. Michael has over 25 years of experience in the IT industry and is a certified ethical hacker. He is passionate about helping clients protect their data and systems from malicious attacks and helping them optimize their online presence and reach. He received a Master’s degree in Cybersecurity and Information Assurance from Western Governors University, and a Bachelor’s degree in Business Administration from the University of Phoenix.

Michael Thompson-Brown

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The best antivirus program is often the built-in one, as it receives daily updates and runs smoothly in the background without consuming excessive resources. These built-in solutions seamlessly integrate with the operating system, ensuring efficient utilization of resources and optimal performance.

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How do I know if my computer has malware?

Michael Thompson-Brown
Cybersecurity Expert
Michael Thompson-Brown is a Cybersecurity Expert based in Portland, Maine. He is the owner and founder of PCRescue!, a company that provides cybersecurity and data management solutions to small businesses and individuals. Michael has over 25 years of experience in the IT industry and is a certified ethical hacker. He is passionate about helping clients protect their data and systems from malicious attacks and helping them optimize their online presence and reach. He received a Master’s degree in Cybersecurity and Information Assurance from Western Governors University, and a Bachelor’s degree in Business Administration from the University of Phoenix.

Michael Thompson-Brown

Cybersecurity Expert

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To determine if your computer has malware, open Task Manager by right-clicking on the taskbar and selecting "Task Manager." In Task Manager, navigate to the "Processes" tab and scan through the list for any unfamiliar or suspicious processes and applications. Look for processes with random or nonsensical names, high CPU or memory usage without any apparent reason, or processes running from unfamiliar locations on your system. These could indicate the presence of malware, and further investigation or removal may be necessary.

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I got a notification that I got a Zeus virus and I called and they said that I have a trojan and that it costs 100 dollars to fix. Is this a scam?

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Yes, this is a scam.

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If a pop-up advertisement prompts you to download anti-virus software, do not install it. This is a common trojan horse tactic. Stick to known products like those mentioned in this wikiHow.

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If you're using an antivirus program that doesn't do regular scans in the background automatically, make sure to turn the "automatic scanning" feature (or similar) on.

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