What is a computer Trojan?

Every day new malware surfaces that can infect our equipment and systems. There are various types of malicious software or code with different characteristics, but they all share a harmful intent. We are talking about viruses, worms, spyware and also trojans. What is a trojan and how does it work?

What is it?

In computing terms, a trojan is a type of software or malicious code that masquerades as another programme that is widely known and in common use, hence its very appropriate name. The history of the use of this term to refer to this type of malware dates back to the 1970s, although it became popular and more established as the use of computers and the Internet became more commonplace and universal in the 1980s and 1990s.

Malicious activities are often carried out in the background, while at the same time imitating the functionality of the programme or application it is pretending to be, often without arousing the suspicion of the computer system owner.

Trojans camouflage their real purpose very well, they are very effective and their spread is sometimes associated with downloading free versions of paid programmes from unreliable sites, and that is how they take advantage of this to infiltrate our computer or device without being detected.

How do computer trojans work?

Some of the harmful activities a trojan can accomplish are:

  • Set up or open a back door into our equipment or systems that allow unauthenticated access and which avoid the access control measures.
  • Install keyboard reading applications, which log and send what we type and allow the attacker to obtain sensitive data such as passwords or credit card numbers.
  • Install a rootkit that allows it to remotely execute operations in equipment and systems or extract sensitive information.
  • Upload files to the affected equipment and systems and infect them with other types of malware.
  • Install software to turn the computer or system into a bot in a botnet.

How do I remove it if my computer has been infected?

As a rule, trojans can be disinfected using antivirus software and programmes specially designed for cleaning some types of trojan.

  1. Install and run an antivirus software.
  2. After analysis and disinfection, restart the PC in safe mode.
  3. The antivirus system will inform you of the need to remove any affected programmes and extensions installed on your computer.
  4. If the antivirus does not work, we recommend formatting your computer.

Tips to protect yourself from these computer viruses

To defend your equipment and personal data from trojans, it is advisable to follow a number of useful security measures, which are the same as for malware in general:

  • Training and awareness for employees in the area of good security practices.
  • Installation and regular updating of anti-virus software for the equipment and systems.
  • Antivirus services for inbound and outbound email and implementation of policies for the acceptance or refusal of attachments.
  • Updating and security patching of operating systems, firmware, applications, etc.
  • Monitoring of network traffic and system behaviour.
  • Scanning, analysis and fixing of vulnerabilities in the systems and applications.

RATs: remote access trojans

RATs or Remote Access Trojans are malicious software that runs on computers and systems and allows intruders to use them remotely. They are designed to be installed and operated in a stealthy (and difficult to detect) manner, usually hidden in Java applets or ActiveX controls that are downloaded while browsing web pages that make use of them.

Examples of RATs are Sakula, DkW0rm, Havex, Dark Comet, etc. Once loaded on the victim's computer or system, the intruder can use it at will.

Trojans are a common method of committing bank fraud and personal information theft. To avoid their proliferation it is advisable to keep your equipment up to date and follow good computer security practices.


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