A Trojan Horse, or simply a Trojan, is a type of malicious software that disguises itself as a legitimate or benign application. The term is derived from the ancient Greek story of the deceptive wooden horse used to infiltrate the city of Troy. Similarly, a Trojan Horse in computing deceives users into executing it, thereby allowing the malware to perform harmful actions on the infected system. 

Characteristics of Trojan Horses

1. Deceptive Appearance; Trojans often masquerade as legitimate software or files, tricking users into downloading and installing them, increasing the likelihood of users unintentionally executing the malware.

2. Payload Delivery; Once executed, a Trojan delivers its payload, which can vary from stealing data to providing unauthorized access. The payload can cause significant harm, depending on its design and intent.

3. Non-Self-Replicating; Unlike viruses and worms, Trojans do not self-replicate or spread on their own. They rely on user interaction and social engineering tactics for distribution.

Types of Trojan Horses

1. Backdoor Trojans

These Trojans create a backdoor entry point on the infected system, allowing remote access and control. Examples: Netbus, Back Orifice.

2. Banking Trojans

Specifically designed to steal banking information, such as login credentials and financial data. Examples: Zeus, SpyEye.

3. Ransom Trojans (Ransomware)

Encrypt files on the infected system and demand a ransom for decryption. Examples: Cryptolocker, WannaCry.

4. Remote Access Trojans (RATs)

Provide the attacker with complete control over the infected system. Examples: DarkComet, PoisonIvy.

5. Downloader Trojans

Download and install additional malicious software onto the infected system. Examples: Emotet, Dridex.

6. Infostealer Trojans

Designed to steal personal information such as passwords, files, and system information. Examples: FormBook, Lokibot.

7. DDoS Trojans

Use the infected system to launch Distributed Denial of Service (DDoS) attacks. Examples: Mirai, Trinoo.

8. Spyware Trojans

Monitor user activity and send collected data back to the attacker. Examples: FinFisher, SpyAgent.

Methods of Infection and Prevention

1. Email Attachments

Trojans are often distributed through malicious email attachments.

Do not open attachments from unknown or suspicious senders.

2. Malicious Downloads

Downloading software from untrusted or compromised websites can lead to Trojan infections. Download software only from reputable sources.

3. Social Engineering

Attackers use deceptive tactics to trick users into installing Trojans.

Be cautious of unsolicited messages and offers that seem too good to be true.

4. Infected Websites

Visiting compromised websites can lead to drive-by downloads of Trojans.

Use updated browsers and security software to block malicious sites.

5. Software Bundling

Trojans can be bundled with legitimate software and installed inadvertently.

Pay attention during software installation and opt out of additional offers.

Symptoms of Trojan Infection

1. Slow System Performance

The computer runs slower than usual as the trojans consume system resources to execute malicious activities.

2. Unexpected Pop-ups

Frequent and unexpected pop-up ads or messages. Some Trojans display ads to generate revenue for attackers.

3. System Crashes

Frequent system crashes or blue screens due to the trojan destabilizing the operating system.

4. Unusual Network Activity

Increased or unusual network activity. Trojans may communicate with a remote server or download additional malware.

5. New or Missing Files

Appearance of new files or disappearance of existing files. Trojans can create, modify, or delete files as part of their payload.

6. Disabled Security Software

Antivirus or firewall settings are disabled without user action as the trojans avoids detection. 

Prevention and Protection

1. Install and Update Antivirus Software; Use reputable antivirus software to detect and remove Trojans.

2. Keep Software and Systems Updated; Regularly update the operating system, applications, and security patches.

3. Avoid Suspicious Links and Downloads; Do not click on suspicious links or download files from untrusted sources.

4. Use Strong Passwords and Enable Two-Factor Authentication; Create strong, unique passwords for all accounts and enable two-factor authentication (2FA).

5. Enable Firewalls; Use firewalls to block unauthorized access to your computer.

6. Regular Backups; Regularly back up important data to a secure location.

7. Educate Yourself and Others; Stay informed about the latest threats and safe computing practices.

Trojan Horses are a significant threat to computer security, capable of causing extensive damage and data loss. Understanding their characteristics, methods of infection, and preventive measures is crucial for safeguarding your systems and data. By staying vigilant and employing robust security practices, individuals and organizations can mitigate the risks associated with Trojan Horses.