What is Trojan malware? The Definitive Guide (2023)

What is a Trojan (horse)?

Trojan horse malware is a file, program, or piece of code thatseems to be legit and safe but it is actually malware. Trojans are packaged and delivered within legitimate software (hence the name) and are usually designed to spy on victims or steal data. Many Trojans also download additional malware after you install them.

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    What is Trojan malware? The Definitive Guide (1)

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      The Trojan horse is named after theTrojan Horsein the Greek epic poemIn IliadIn the story, the Greek hero Ulysses outlines a plan to build a gigantic wooden horse that his enemies - the Trojans - would receive as a gift in their city. But inside the horse's belly hid a legion of soldiers, who emerged in the dead of night to decimate the city of Troy from within.

      Trojan malware works the same way -pretends to be something harmless, but it is just a cover for its real and malicious intent.To stay protected against trojans and other malware, downloadfree antivirus software for windows 10orWindows 11.

      How do Trojan horses work?

      Trojans work under the guise of legitimate files, with the aim of tricking victims into clicking, opening, or installing them. When this happens, the Trojan starts installing malware on your device,spying on you, or causing other types of damage.

      For example, email trojans will usesocial engineering techniquesto mimic mundane email attachments. The email itself will also appear trustworthy, but it is actually a fraudulent email sent by acybercriminal. When you open the attachment, the Trojan gets activated and starts attacking your device. Deception is a central part of the Trojan horse definition.

      Is a Trojan a virus or malware?

      Trojan horses are notvirus, but theythey area type ofmalware. People sometimes refer to it as a “Trojan virus” or “Trojan horse virus”, but it doesn't exist. This is due to a critical difference in how viruses and Trojans infect victims. While viruses self-replicate, spreading from one victim to another, Trojans need you to install them.

      This distinction is what distinguishes viruses from Trojan horse malware. Of course, viruses and Trojans themselves are types of malware.

      What is Trojan malware? The Definitive Guide (2)Trojans are not viruses but are a type of malware.

      How to recognize a Trojan attack

      Trojans are sneaky, but if you know what to look for, you can recognize the signs of a Trojan attack and start the debugging process.trojan removal. Here are the most common signs of a Trojan malware attack:

      • Your computer seems slow

        Trojans often install additional malware that together can consume a large amount of computing resources. Remove Trojan malware infection forspeed up your pcor another device.

      • hangs and freezes

        Trojan horses can sometimes overload your computer andcause failuresor other faults. The infamous Blue Screen of Death is always a cause for concern.

      • Unknown apps on your device

        Many Trojans install additional malware. If you notice something strange in Task Manager in Windows or Activity Monitor in macOS, look it up - it could be malware.

      • internet redirects

        Some Trojan Horseschange your DNS settingsor manipulate your browser to redirect you to malicious websites that may collect your data or infect you with additional malware.

      • Changes to your desktop, taskbar, or browser

        As the Trojan installs new malware or makes other changes to your computer, you may see new icons on your desktop or taskbar. The same goes for browser toolbars or plug-ins that you didn't install yourself — keep an eye out for them.browser hijackers.

      • More popups

        Are you seeing more pop-ups than usual? A Trojan may have installedadwareon your device.

      • Your antivirus software is disabled

        Trojans and other malware don't want to be detected and removed - so they will try to shut yourantivirus software. Protect yourself against Trojans and other malware with a free antivirus solution that blocks them before they can do harm.

      Avast OneAutomatically detects and blocks Trojan horse infection on your devices. And it will clean all infections currently on your machine. Protect yourself against Trojans and other malware with Avast One, an award-winning antivirus tool.

      Types of Trojan malware

      What is Trojan malware? The Definitive Guide (3)Trojans the backdoor

      Cybercriminals use backdoor Trojans to obtain a “backdoor” on your device — a way to access your computer without your knowledge. This backdoor is often used to install more malware, spy on you and collect your data, or connect your computer to abotnet.

      What is Trojan malware? The Definitive Guide (4)banking trojans

      Banking Trojans infiltrate your devices and steal your financial login credentials.hackersuse them to crack your bank accounts and other financial accounts. The Zeus Trojan — one of the most infamous Trojans to date — was a banking Trojan.

      What is Trojan malware? The Definitive Guide (5)DDoS Trojan Horses

      DDoS Trojans aim to recruit your device into a botnet: a network of linked devices remotely controlled by a hacker known asrobotpastor. They will use the botnet to performDistributed Denial of Service (DDoS) attacksthat shut down other websites and internet services.

      What is Trojan malware? The Definitive Guide (6)Dropper or downloader trojans

      Droppers are the first step in acombined threat— a three-part malware package consisting of a dropper, loader, and more malware (usually arootkit). OdropperTrojan infects your device and sets the stage for thecharger, which in turn installs arootkitthat gives a hacker access to your device. Other download Trojans install other types of malware.

      What is Trojan malware? The Definitive Guide (7)Explore trojan horses

      These rogue trojans usefeats— software tricks designed to take advantage of a known software or hardware vulnerability — to infect your device.zero day exploitstarget vulnerabilities that no one but the creator of the exploit has discovered yet.

      What is Trojan malware? The Definitive Guide (8)Fake Antivirus Trojans

      A dangerous kind ofscareware, fake AV Trojans pretend to detect viruses and other malware on your device, then ask you to pay for security software — which is either useless or actively malicious. When you pay, the Trojan creator gets your payment details.

      What is Trojan malware? The Definitive Guide (9)gaming trojans

      Gaming Trojans Target Onlineplayersand steal your login information. Cybercriminals can use them to crack high-profile players' accounts or steal valuable game items.

      What is Trojan malware? The Definitive Guide (10)Infostealer Trojan Horses

      Data theft is the goal of infostealer Trojans. They scour your device for sensitive personal data and send it back to the hacker who attacked you. Cybercriminals can use this data to commit fraud orIdentity theft.

      What is Trojan malware? The Definitive Guide (11)Instant Messaging Trojans

      Targeting instant messaging (IM) applications on your device, IM Trojans hijack your login credentials and access your contact list. Latest instant messaging apps that usecryptographylike WhatsApp or Signal are less vulnerable than older services like Skype or MSN Messenger — but malware is always evolving.

      What is Trojan malware? The Definitive Guide (12)Mailfinder Trojan Horses

      Less dangerous in the age of webmail services like Gmail, mailfinder Trojans target email applications like Microsoft Office and probe them for email addresses. Cybercriminals can add any stolen email address to theirspamor phishing attacks.

      What is Trojan malware? The Definitive Guide (13)Trojan the ransomware

      ransomwareis a type of malware that blocks your access to your data or device and threatens to publish, permanently retain, or destroy the data unless you pay a ransom. Ransomware Trojans use deception to trick victims into activating ransomware.

      What is Trojan malware? The Definitive Guide (14)SMS Trojan Horses

      SMS Trojans infect mobile devices, usually Android, and send expensive SMS messages to premium services owned by the cybercriminal or intercept messages coming in and out of your phone.

      Examples of Trojan horse attacks

      Trojan horse malware has caused some of the most notorious cyber attacks in history. Here's a look at several of the most well-known Trojans.


      OZeus TrojanIt first appeared in 2007 in a data theft attack on the US Department of Transportation. Primarily known as a banking Trojan, ZeuS is commonly used to steal financial information via two browser-based techniques:

      spread widely viae-mails de phishingand automatic drive-by downloads from infected websites, ZeuS ended up infecting millions of computers - which is why it was used to create Gameover ZeuS, one of the most notorious botnets of all time.

      The emotion

      First detected in 2014, Emotet started out as a banking Trojan. But after cybercriminals started using it to distribute other malware, Emotet made huge waves in cybersecurity.

      Routinely hailed as one of the most harmful strains of malware ever created, Emotet targeted corporate and individual victims through massive spam and phishing campaigns. The malware was used to create multiple botnets, which were then rented into amalware as a service (MaaS)model for other enterprising cybercriminals.

      Emotet was finally discontinued in 2021 through acoordinated global law enforcement effort.

      The witness

      Trojans are not just for Windows - Shedun is an AndroidadwareTrojan horse that repackages legitimate Android apps with fake adware, before rehosting them on third-party download portals. When you install an application from one of these sites, you get adware along with it.

      Once you install the infected application, you are spammed with advertisements that generate revenue for the attacker.Removing Malware from Your Android Deviceit is very difficult and most of the victims have opted to buy new devices. In 2016, Shedun was reported to have infected over 10 million Android devices.

      Can Trojans affect mobile devices?

      Trojans can affect mobile devices as well as desktop and laptop computers. Both Android and iOS have been affected by Trojan horse malware, although Android Trojans are far more common.

      OGriftHorse Trojan Horseis a recent Android SMS Trojan that signs up victims for premium messaging services to generate revenue for the attacker. So far, it has affected more than 10 million victims worldwide. GriftHorse masquerades as legitimate apps - the most popular of which have over 500,000 downloads alone.

      In 2016, orTrojan AceDeceiver for iOSwas able to attack non-jailbroken iOS devices. Three separate AceDeceiver apps passed Apple's internal review processes and were available for download from the official App Store. Learnhow to remove malware from your iPhoneso you are ready if this happens to you.

      Como remover o malware Trojan

      The best way to remove Trojan malware from any device is with expertstrojan removal software. Removing Trojans is similar tovirus and other malware removalFrom your computer.

      1. Download Avast One or other antivirus software from a reputable provider.

      2. Enter safe mode.

        Restart your PC in safe mode to prevent any malware from running or using the Internet.

      3. Remove temporary files.

        Use the Disk Cleanup tool toremove temp files. This will speed up the malware scan you'll be doing next.

      4. Scan your PC for malware.

        Use your ownantivirus softwareto scan your PC for Trojans and other malware. Your software should automatically detect the malware and remove it.

      5. Recover damaged files or data.

        If you regularly back up your computer, restore any damaged files or data from your backup.

      How to Avoid Trojan Horse Attacks

      1. Download apps and software from official sources.

        Trojans are often hosted on third party application download sites. Get your software directly from the manufacturer or from official portals like the Apple App Store and Google Play — although theseterhave been compromised by Trojans in the past, they are much safer than other options.

      2. Do not open unknown email attachments or click on strange links.

        Fraudulent emails are a popular vector for spreading Trojans. Don't click on attachments or links in emails that you don't expect to receive. Even if the email looks legitimate, it could becounterfeitby a cybercriminal.

      3. Use an ad blocker or a secure browser.

        Some trojans spread via infected web advertisements. An ad blocker orprivate browserwill prevent these and other ads from loading in your browser, preventing infected websites from delivering a Trojan horse.

        Avast Secure Browseris a highly secure browser that automatically blocks ads and protects you from malicious downloads.

      4. Be skeptical of free software.

        Trojan horse creators often disguise their trojans as free games and other seemingly useful applications. If you're about to install something new, research it first and read user reviews.

      5. Do not click on unknown web banners or links.

        Not all drive-by downloads are viamalvertising. Some malware writers develop websites that can automatically install Trojans and other malware on your device as soon as you visit. Avoiding unknown websites reduces the risk of downloading a Trojan.

      6. Use an antivirus tool.

        A strong antivirus tool from a reputable provider will automatically keep Trojans off your device. Choose one that works like amalware removal toolwhich can detect and remove trojans and other malware from your devices as well.

      Defend against Trojans with comprehensive security

      While there are many types of Trojan horse malware, all aredesigned to trick you into installing them. This is why Trojans can be so difficult to detect — they look like legitimate software.

      The best way to protect yourself against Trojans is with reliable security software that can detect, block, and remove all types of malware and viruses automatically. This way, there is no chance of the Trojan tricking you. Get rid of trojans today withAvast One, an award-winning antivirus and cybersecurity solution that is 100% free.

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