17 types of Trojans and how to defend against them

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Computer Trojans received their name from the infamous mythological horse. The Trojan’s basic mission is to mislead people of its real goal. A Trojan is malicious software that usually needs to be launched by the user or another malicious program.

Malicious code typically penetrates the system under the guise of a useful utility or tool. However, the main task of such software is to perform one or more of these malicious actions:

  • Delete user or system data
  • Change user or system data
  • Encrypt user or system data
  • Copy user or system data
  • Send and receive files
  • Slow computers
  • Slow networks

Trojans have evolved into different complex forms like backdoors (that can manage distant computers) and downloaders (that can download and install other malicious programs. These are the types of Trojans that you need to be aware of:

1. ArcBombs

These Trojans represent special archives that are designed to behave abnormally when users try to unpack them. ArcBomb archives either freeze or seriously slow the system. Malicious archives use different techniques to achieve their goal. They may use malcrafted headers or corrupt data that lead to a malfunction of an archiver or an unpacking algorithm. They may also contain a heavyweight object that consists of identical, repeating data that can be packed into a small archive. For example, 10 GB of data is packed into a 400 KB archive.

2. Backdoors

Backdoors allow criminals to control computers remotely. Attackers can do a wide range of actions on an infected computer including receiving, sending, deleting or launching files; displaying screen alerts; or rebooting PCs. These Trojans can also help attackers install and launch third-party code on the victim’s device, record keystrokes (acting like keyloggers), or turn on the camera and microphone. Sometimes backdoors are used to manage a group of infected computers (or recently IoT devices) united into a botnet.

A separate type of backdoor can spread over the network (just like a worm). Unlike woks, they do not spread by themselves, but only after receiving a command from their creator.

Copyright © 2021 IDG Communications, Inc.



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