Internet, Networking, & Security Antivirus What Is a Trojan Virus? What a trojan virus is and how you can avoid getting one By Ryan Dube Writer Ryan Dube is a freelance contributor to Lifewire and former Managing Editor of MakeUseOf, senior IT Analyst, and an automation engineer. our editorial process Facebook Twitter LinkedIn Ryan Dube Updated December 07, 2019 Antivirus Browsers Cloud Services Error Messages Home Networking 5G Antivirus VPN Web Development Around the Web View More Tweet Share Email A Trojan virus is actually not a virus at all. It's a malicious software you may inadvertently download, thinking that you're installing a legitimate program. The purpose of trojan software is either to extort or steal money from you or take control of your computer for mischievous purposes. Trojans vs. Viruses Couleur / Pixabay The best explanation of the difference between trojan software and a virus or malware is the story about the Trojan War and the Trojan horse. What is a Trojan horse? As the story goes, the Greeks constructed a huge wooden horse filled with soldiers and presented the horse as a parting gift to the City of Troy. Once the horse was inside the city, the Greek soldiers crept out of the hollow horse and attacked the city under cover of darkness. Viruses are software that are created to infect one computer and then spread to other computers. Trojan software isn't created to spread. It's meant to perform a very specific task on your computer or mobile device. What Is a Trojan Virus? A Trojan virus is meant to perform malicious tasks on your computer, usually without you even knowing it. These tasks might be to: Provide hackers with a back door to take control of your computer.Intercept your internet traffic to steal bank account or credit card information.Join your computer into a larger internet "botnet" to perform criminal activity like Denial of Service (DDoS) attacks.Corrupt your system files and make your computer unresponsive so the hacker can extort money from you.Harvesting email addresses or phone numbers that hackers then sell to spammers. Trojans can be very expensive. One of the most famous trojans was the FBI MoneyPak virus, which made users' computers unresponsive and advised users to send from $200 to $400 to restore their system. Unfortunately, many people paid the hackers. How You Can Get a Trojan Westend61 / Getty Images Unfortunately, getting a trojan virus is as simple as downloading the wrong application onto your computer or mobile device. Even if you never download software, it's still possible to inadvertently transfer one of these malicious applications to your computer. If you take any of the following actions, you could make yourself vulnerable to a trojan attack. Click on a link in an email that downloads an application to your computer.Downloading "free" software from websites that you don't recognize.Clicking on website pop-up ads.Downloading files off the dark web.Sharing or downloading Bittorrent files. The bottom line is that any time you place a file onto your computer from a website or any other source that you don't recognize, you're putting your computer at risk for a trojan attack. How to Avoid a Trojan Virus Viruses and malware can be annoying, but there are few things quite as damaging as a trojan virus. When your computer gets infected by one of these, it can be difficult to impossible to remove. The best defense is to avoid getting infected by one at all. Here is how you can avoid getting a trojan virus on your computer or mobile phone. Install high-quality antivirus software.Enable automatic Windows Updates to keep your OS always patched.Use email services that automatically scan attachments for viruses like Gmail's attachment scan feature.Never click on email links, or test suspicious links before clicking on them.Avoid visiting websites that are only set up for hosting free software.Never download files off the dark web.Use ad-blocking browser addons, and whitelist only known, safe websites. Your Best Defense Is a Good Backup Even the most careful users can end up infected with a trojan. The best way to defend yourself is to never leave yourself entirely dependent on files stored on your computer. Use backup software to take a full backup of your computer system. At the very least, make sure to only store important files on external hard drives, and keep those drives disconnected from your computer when you don't need the files. With a full system backup, if a trojan ever takes over your system and hackers attempt to exploit you for money, you can perform a full system recovery and get rid of those hackers for good.