CompTIA A+® Certification All-In-One For Dummies®, 2nd Edition

3.2. Understanding Malicious Software

Other types of malicious software, outside of your typical viruses, attack systems every day. The following sections outline other types of malicious software — but understand that they are all considered types of viruses.

3.2.1. Trojan horses

Trojan horses are special programs that do something totally different than what the user who runs it thinks it does. For example, NetBus is a very popular Trojan virus that ships as a file called patch.exe. A hacker e-mails the file called patch.exe and explains in the e-mail that this is a security patch you need to apply to make sure your system is secure. Unfortunately, patch.exe is the security hole! When you run patch.exe, it opens your system up to the hacker by opening a port so that the hacker can connect to the port at any time and control your system.

Trojan viruses are normally loaded on your system by the hacker tricking you into running the program on the system, typically through an e-mail message. You can remove the Trojan with virus protection software.

3.2.2. Worms

A worm is a self-replicating virus: The worm doesn't need to be activated by the user opening the file. Rather, a worm is a virus that runs on a system and also tries to infect other systems on the network. The Nimda virus is an example of a worm virus.

Worms are loaded on your system by connecting to your system across the Internet. The worm is usually designed to infect the system by connecting through a specific piece ...