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Computer Viruses, Trojans, Worms, Adware, Spyware and Malware:
      »What's the Difference?

If you've spent a decent amount of time online, you've probably heard many different terms being bandied about concerning PC infections. Things like Computer Viruses, Worms, Malware, Spyware and Trojans may sound interchangeable, but they're actually not. Each infection has its own unique set of characteristics. While Adware, Spyware, Trojans, Worms and Viruses are all types of Malware, each term refers to something completely unique. If you're tired of scratching your head about what all of these different terms mean, the following information is sure to come in handy.


The term Malware is derived from two different words - "malicious" and "software." That fact alone tells you that its an umbrella term under which many different types of malicious PC programs fall. If you're not sure whether you're dealing with a Trojan or a Worm, referring to it simply as "Malware" is perfectly acceptable. Indeed, Malware is a general term for any kind of program that is designed to harm your computer. Adware, Spyware, Trojans, Viruses and tracking cookies are all types of Malware.

Computer Viruses

The most notable characteristic of a Computer Virus is that it attaches itself to a legitimate program or file to perform its damage. Most of the time, computer viruses attach themselves to executable files (files ending with .EXE); those files and programs must be run in order for the virus to work. Viruses can copy themselves and spread quickly. They are transmitted through computer networks, the Internet and portable media like USB drives, DVDs and CDs. You can receive computer viruses via email or by copying a program onto a CD and installing it onto your PC.


As the name implies, a Trojan is a type of virus that appears utterly innocuous; many times, it even looks like an exciting new game or a useful new program. Once installed, though, Trojan Horses can cause some serious damage. In some cases, a Trojan might only cause mild problems; unimportant changes to your desktop, for instance, could occur. Other times, though, serious trouble can arise. In the worst case scenario, a Trojan can create a "backdoor" on your PC that a hacker can use to get into your system. From there, the hacker can enjoy free access to your computer system and cause all sorts of mayhem. Unlike viruses and worms, though, Trojans cannot replicate or duplicate themselves.


A Worm is also a type of computer virus. As such, it can replicate itself with ease. The kicker, though, is that they can do so without human assistance. You don't have to run an executable program in order to unleash the wrath of a worm. Worms travel across computer networks and create hundreds of copies of themselves. Those copies can be transmitted through the network yet again, replicating themselves as well. In short order, hundreds - or even thousands - of copies of a worm can be created. They suck up a lot of system memory and are known to crash entire networks.


Spyware is a kind of malware; it has a specific objective, though: Running in the background to gather information from your computer system. That information can include anything, from financial data to passwords and login information. Key loggers, which record every key that you press, are commonly used in spyware situations. The information that is gathered is sent through your Internet connection to a hacker who can use it as he sees fit. Needless to say, spyware isn't something that you want running on your computer.


As its name suggests, Adware is a word formed from combining "Advertising" and "Software." In essence Adware is advertising-supported software. These advertisements are often in the form of pop-ups and help generate revenue for the software author. Adware is more annoying than harmful on its own, but often times Adware comes bundled with other unwanted software such as Spyware.

As you can see, a computer can become infected by any number of troubling things. There's a simple way to significantly reduce your risk of encountering such issues, though: using a first-rate anti-spyware and antivirus program. With all of these sophisticated programs out there, leaving your PC unprotected really is a recipe for disaster.

Article last updated May 15, 2011.

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