Category: Malware

Type: Trojan

Aliases: Trojan, Trojan:W32/[variant], Trojan.win32


Named after the Trojan Horse of Greek legend, a trojan is a program or file that has, or appears to have, a useful or desirable function to encourage the user to install the program or open the file. In the background however, it also silently performs unauthorized actions (its payload), without the user's knowledge or consent.


Automatic action

Based on the settings of your F-Secure security product, it will either automatically delete, quarantine or rename the detected program or file, or ask you for a desired action.

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Technical Details

A trojan is usually deliberately designed by its author to appear authentic and attractive. For example, it may appear to be a screensaver, a service pack, an application update and so on.


Trojans rely on tricking the user into believing that the program is authentic, so that they unwittingly install the program themselves. To do this, most trojans mimic or entirely copy the style and branding of popular legitimate programs or files. Some trojans (particularly on the Android platform) are actually copies of legitimate apps that have been repackaged or trojanized to include harmful components.

Trojans are often distributed using the same (or very similar) names and designs as popular programs, to increase the chances that users will mistake the trojan for the legitimate app and install it instead.

Once installed or opened, the trojan may perform its promised function, or display a decoy document to distract the user. In the background however, it also silently performs unauthorized actions (its payload), without the user's knowledge or consent.


Depending on its creator's intent, a trojan's payload can range from:

  • Mildly annoying pranks, like changing desktop icon positions, to
  • Serious, user-inhibiting actions, like disabling the keyboard or mouse, to
  • Critically destructive actions, like erasing files or stealing data

It is often very difficult for users to realize that a trojan is performing harmful actions, as they are usually well camouflaged to keep the system from triggering any notification messages that might arouse the user's suspicions.

Types of trojans

Trojans are often classified into sub-types based on the actions they perform. These are just a few of the possible types:

  • Trojan-downloader
    Contacts a remote server and downloads other harmful programs from it
  • Trojan-dropper
    Contains one or more harmful components that it drops and installs
  • Trojan-spy
    Monitors activity on the device, or steals content from it
  • Password-stealer
    Steals passwords and other confidential details from the device
    • Banking trojan - A specialized type of password-stealer, banking trojans monitor or intercept connections to online banking sites
About Ransomware

A specialized type of trojan is ransomware, which attempts to steal, delete or encrypt the user's own files; the user must subsequently 'ransom' these files back from the attacker, usually by monetary payment. For more information about this type of malware, see:

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