Threat Descriptions

Trojan

Classification

Category :

Malware

Type :

Trojan

Platform :

W32

Aliases :

Trojan.[variant], Trojan:w32.[variant], Trojan.win32.[variant], win32.[variant]

Summary

A program or file that appears to be useful, desirable or legitimate, but performs unauthorized actions (its payload) without the user's knowledge or consent.

Removal

Based on the settings of your F-Secure security product, it will either move the file to the quarantine where it cannot spread or cause harm, or remove it.

A False Positive is when a file is incorrectly detected as harmful, usually because its code or behavior resembles known harmful programs. A False Positive will usually be fixed in a subsequent database update without any action needed on your part. If you wish, you may also:

  • Check for the latest database updates

    First check if your F-Secure security program is using the latest updates, then try scanning the file again.

  • Submit a sample

    After checking, if you still believe the file is incorrectly detected, you can submit a sample of it for re-analysis.

    Note: If the file was moved to quarantine, you need to collect the file from quarantine before you can submit it.

  • Exclude a file from further scanning

    If you are certain that the file is safe and want to continue using it, you can exclude it from further scanning by the F-Secure security product.

    Note: You need administrative rights to change the settings.

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.

Installation

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.

Impact

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-stealerSteals passwords and other confidential details from the device

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: