If you're reading this article, you probably know that viruses, Trojan Horses, and spyware are all harmful to your PC. The purpose of this article is to differentiate between different types of Malware (malicious software) so that PC users can have a better understanding of what might be wrong with their PC's, or at least be able to understand techies when they tell you that your PC is infected with one or more types of Malware.

Lets start with a basic definition of Malware. Malware is defined as a broad-spectrum term to describe any software engineered to cause damage to a single computer, server, or computer network. Malware includes viruses, Trojan Horses, and spyware.

We all learned in junior high biology that a virus is an organism that seeks out a host from which to replicate itself. Computer viruses are no different. Computer viruses are programs or scripts that attempt to spread from one file to another (on a single computer) and/or from one computer to another without the knowledge and consent of the user. There are several methods of propagation, although they will not be discussed in this article. While there can be obvious incidental damage, viral damage is often unintentional and due to the fact that the author failed to anticipate the full effect of the virus or consider possible side-effects.

Virus scanners are the most common tools used to prevent acquisition of viruses. A virus scanner examines a program before it runs, and if it detects any malicious code, it will shut down the program immediately. The best way to avoid getting viruses is to not download any executable files when you are unsure of the source.

In Greek mythology, the Trojans used a horse to disguise/camouflage their soldiers. Similarly, a Trojan Horse when referring to PC's is a program or script which appears as one thing, when it is actually another. Trojan Horses fit the definition of a virus in that they infiltrate PC's without the knowledge or consent of the user. However, while harm from viruses can often be unintentional, harm from Trojan Horses is not unintentional. Trojans typically do one of the following:

1. Modify or destroy data
2. Steal confidential information (passwords, credit card numbers, etc.)

Virus scanners are the most common tools for prevention against Trojans, as many of them have methods for dealing with such infections. Again, the best way to avoid contracting Trojans is to practice safe computing.

Spyware is software installed on a computer that is able to track habits and relay such information to tailor advertisements, pop-ups, etc. Spyware is a bit different from viruses and Trojans in that it does not spread from computer to computer or from file to file. Rather, it is often installed by the user in conjunction with freeware/shareware. Remember the big Kazaa craze? Well, every user who installed Kazaa was also installing spyware on their computer. Unfortunately, because very few people read the license agreement, they were unaware that spyware was being installed on their system.

Detection programs such as Ad Aware can be used to determine if a system is infected with spyware. These programs work like virus scanners. The best way to prevent acquisition of spyware is to use discretion as to which programs you should install, as well as reading the entire license agreement to ensure you are not agreeing to something you don't want.

Again, practicing safe computing is the best way to keep your computer running well and avoid infecting your system with harmful Malware.