Trojan Horse

A trojan horse, or trojan, is a form of malware that disguises itself as a harmless file or application to mislead users of its true objective. The trojan will be released on the user s device with a click or download of the seemingly innocent program. This allows the malicious code to perform whatever task the attacker intended. Unlike viruses and worms, trojans do not reproduce or self-replicate.

The name for this malware comes from the Greek legend of the Trojan War, in which the Greeks gift the Trojans a giant, wooden horse. After the horse was accepted into Troy s city walls, Greek soldiers emerged from their hiding place within the horse and opened the city gates, which led to the capture of the city.

Types of trojan horses

  • Backdoor allows attackers full access and control of the computer it infects.
  • Banker steals banking account information.
  • Data Sending sends sensitive data from a device to the attacker by searching the device or keylogging.
  • Distributed denial of service (DDoS) uses multiple devices infected by trojans to overwhelm and flood a network which leads to a denial of service.
  • Destructive trojans destroy and delete files.
  • Downloader trojans download and install malicious software and programs.
  • Game-thief steals online gamer s account information.
  • Mailfinder steals email addresses from your mail history.
  • Proxy trojans use the infected computer as a proxy or zombie to conduct illegal activities undetected.
  • Ransom trojans steal data or damage your computer, and the attacker requires a ransom to release your data or repair the damage.
  • Rootkit hides the malware on your device to extend the time that the program can run.
  • SMS infects a mobile device and can send and intercept text messages.

How to avoid trojan horses

As you can see from the list above, trojans can steal sensitive information and cause a lot of serious damage. Fortunately, there are a few steps you can take to avoid this malware:

  • Don’t open an attachment or run a program found in an email from an unknown sender.
  • Only download software from sources you fully trust.
  • Avoid clicking on pop-ups that promise free software.
  • Keep your computer and its software up to date.
  • Install and regularly run an antivirus program on your computer.

Signs of a trojan horse

  • Desktop changes
  • Increase of spam or pop-ups
  • Poor device performance
  • Unfamiliar downloads, add-ons, or applications
  • Changes to display color, clarity, or orientation
  • Strange device behavior

Vangie Beal
Vangie Beal
Vangie Beal is a freelance business and technology writer covering Internet technologies and online business since the late '90s.

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