What is Malware? - Definition, Examples & Types

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  • 0:02 Malware
  • 0:47 Types of Malware
  • 3:01 Preventing Malware
  • 4:07 Lesson Summary
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Lesson Transcript
Instructor: Christopher Nott

Christopher has taught college level information technology and IT security, has a master's degree in Information Security, and holds numerous industry certifications.

Viruses, worms, spyware, adware, hijackers, and Trojans. What do all of these things have in common? They're all forms of malware. In this lesson, we'll define malware and discuss some common types and examples.


We've all heard about computer viruses. We've probably all had one at some point. But we're increasingly hearing about different malicious computer software, like worms, spyware, adware, hijackers, and Trojans, and these terms confuse a lot of people. This lesson will help clear up the confusion.

There are so many new threats to computer systems that we've created a general term to describe them all. That term is malware. Malware is a combination of the words malicious and software and is used to describe, in general terms, any type of bad code we may find on a computer. Any software that gets installed on your machine that performs some unwanted or harmful task, normally for the benefit of some third party, qualifies as malware.

Types of Malware

Now that we know what malware is, let's look at the most common types of malware, including viruses, worms, spyware, adware, hijackers, and Trojans.

A computer virus is a piece of software that can be attached to another program or file. This program or file is said to be the host. Much like a human virus infects the body by attaching itself to a cell, a computer virus may attach itself to a file that is downloaded and installed on your computer. The virus spreads when the infected file is passed from system to system. Normally viruses are written to do harm to your computer, like destroy system files.

A computer worm is very similar to a virus. The design is the same but, unlike a virus, a worm is capable of moving from system to system without any human action. Worms replicate themselves on your system, attaching themselves to different files and looking for pathways between computers, such as a computer network that shares common file storage areas. Like viruses, worms are often associated with causing damage to computer systems.

Spyware may be spread like a virus or a worm, but spyware has a special classification because its purpose is to steal private information from your computer for a third party, like a spy. Spyware works in a number of different ways.

Adware is like the other forms of malware we've discussed, but its purpose is to display those annoying pop-up advertisements. Adware can be bundled with legitimate software or can be hidden inside other software we download and install. The purpose of adware is to get you to click on the ad it's presenting so that some third party may get paid just for the click.

A hijacker is adware that attaches itself to your web browser, like Internet Explorer, Firefox, or Chrome, and displays intermittent advertising in your browser either by creating pop-ups or by injecting advertising directly into the pages you're browsing. This malware also commonly changes your browser settings, like your preferred search engine or home page and may install browser helper objects like toolbars that track your browsing habits.

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