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A Trojan horse is a type of malicious software that masquerades as harmless or useful software in order to sneak onto a computer system undetected. Once installed, it can perform malicious actions such as stealing data, tampering with the system, or installing other malware. Unlike a virus, a Trojan horse does not replicate itself, but instead requires the active consent of the user in order to install.
How does a Trojan horse work?
A Trojan horse works by disguising itself as harmless or useful software in order to trick the user into installing it on their computer. Once the Trojan is executed, it performs its malicious function in the background. The exact process can vary depending on the type and purpose of the Trojan, but the basic process is as follows:
- Distribution and camouflage
A Trojan masquerades as a legitimate program, game, update or document that the user wants to download. Trojans are often distributed via email attachments, fake software downloads, infected websites, social media or phishing attacks.
- Installation
As soon as the user opens the supposedly harmless attachment or file, the Trojan is installed. This usually goes unnoticed because the Trojan disguises itself as a normal application. During the installation process, the Trojan can penetrate deep into the operating system to perform its functions and prevent itself from being detected.
- Execution of malicious functions
Depending on the type of Trojan, it can perform a variety of harmful actions, such as:
- Data theft: The Trojan horse can read sensitive information such as passwords, credit card details or other personal data and transmit it to the attacker.
- Remote control: It allows the attacker to remotely control the infected computer, manipulate files or install other malware.
- Spying: Some Trojans can monitor keyboard entries (keylogger), take screenshots, or activate the microphone and webcam.
- Malicious updates: The Trojan can download and install other malware, such as ransomware or spyware.
- Remain undetected
Many Trojans use techniques to hide their presence, such as by encrypting their files or hiding in system processes. Some Trojans are able to disable antivirus software or impair its functions in order to remain undetected.
- Communication with the attacker
A Trojan can establish a connection to a so-called command-and-control server (C&C), through which the attacker sends commands to the Trojan and receives data from the infected system. This communication often takes place via encrypted channels to avoid detection by security software.
What types of Trojans are there?
There are different types of Trojan horses that are classified according to their purpose and the functions they perform.
- Backdoor: A backdoor Trojan opens a so-called “back door” on the infected computer that allows an attacker to control the system remotely. This type of Trojan is often used to secretly install other malware, steal confidential data, or use the computer for criminal activities.
- Banking: Banking Trojans are specifically designed to steal sensitive information related to online banking. They can intercept passwords, account details and credit card information and forward them to the attacker in order to cause financial damage.
- Ransomware: Ransomware Trojans encrypt the data on the infected computer and demand a ransom to release it. These Trojans are particularly dangerous because they block access to important data, allowing for the blackmail of the user or entire companies.
- Spyware: A spyware Trojan specializes in spying on the user by collecting information about their activities. This type of Trojan monitors, for example, keystrokes, websites visited and passwords stored in order to steal confidential data.
- Downloader Trojans: Downloader Trojans are designed to download other malicious programs from the Internet and install them on the infected computer. They are often used as precursors to download other malware such as ransomware or keyloggers.
- Trojan Dropper: A Trojan Dropper is designed to place other malicious programs or files on a system without being detected by security software. It disguises the malicious components to prevent their detection and to install the malware unobtrusively.
- Remote Access Trojans (RATs): A Remote Access Trojan allows the attacker to remotely control the infected computer and access all its data and functions. RATs are often used to steal files, install programs or monitor computer activity.
- Rootkit: Rootkit Trojans are particularly dangerous because they hide the existence of other malware on the infected computer. They manipulate system processes and files so that neither the user nor security software can easily detect the infection.
- Fake antivirus Trojans: A fake antivirus Trojan deceives the user by posing as legitimate antivirus software. It displays fake alerts about alleged threats and tries to trick the user into buying useless software or revealing personal information.
- Trojan GameThief: Trojan GameThief specializes in stealing login credentials and other information from online games. It aims to steal game accounts or virtual currencies that can then be sold or exchanged for real money.
- Trojan-Mailfinder: Trojan-Mailfinder searches the infected computer for email addresses and transmits them to the attacker. These addresses are often used for spam or phishing campaigns to send fraudulent messages.
- DDoS Trojans: A DDoS Trojan uses the infected computer as part of a botnet to carry out targeted attacks on a website or server. The aim is to paralyze a website or online service by massively overloading it with traffic.
How do you recognize a Trojan?
Detecting a Trojan horse on a computer can be difficult because they are often designed to go unnoticed. However, there are some signs that may indicate that a system is infected by a Trojan horse.
- Slow system performance: If your computer is suddenly running much slower than usual, programs are taking longer to launch, or you are experiencing frequent crashes, this could indicate malware running in the background.
- Unusual pop-ups and ads: Sudden pop-ups, alerts, or ads that weren’t there before may be a sign of infection.
- Unknown programs or processes: If programs that were not downloaded are installed on the computer or unknown processes are running in the task manager, this may indicate a Trojan.
- Increased network activity: An unusually high level of Internet activity, even if no programs are actively accessing the network, may indicate that a Trojan is sending or receiving data.
- Changes to files: Files that are suddenly missing, encrypted or have been changed may indicate an infection.
- Disabled security software: If your antivirus software or firewall is suddenly disabled for no apparent reason, this could be a sign that a Trojan is trying to hide from detection.
- Unusual messages or error messages: If you frequently encounter error messages or notifications that you do not understand, a Trojan may be active in the background.
How can you protect yourself from a Trojan horse?
Protection against Trojans requires a combination of safe behavior on the Internet and technical security measures. Reliable antivirus and antimalware software is essential, which should be updated regularly to detect and remove known Trojans and other malware. It is equally important to keep the operating system and all installed programs and apps up to date to close security gaps that could be exploited by Trojans.
Particular caution is advised when opening emails and attachments, especially if they come from unknown or suspicious senders. Even supposedly trustworthy messages should be viewed with skepticism, as sender addresses could be faked. Software and files should only be downloaded from official websites or reputable app stores to minimize the risk of infection by Trojans.
An activated firewall helps to prevent unauthorized access to the system by monitoring incoming and outgoing network connections and blocking suspicious activity. Unfamiliar links in pop-ups or ads or on questionable websites should be avoided. Pop-up blockers and ad blockers can help by blocking potentially harmful ads and pop-ups.
Checking the access rights of installed programs also plays an important role in protecting against Trojans. Software that demands unnecessarily extensive administrator rights or access to confidential areas of the system should not be installed. Regular backups of important data ensure that lost information can be restored in the event of an infection. These backups should ideally be stored on an external storage device or in the cloud.
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