Types of Computer Viruses: Functions & Examples

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  • 0:04 Computer Viruses
  • 1:16 Boot Sector, Program, Macro
  • 2:14 Hijacker, Direct…
  • 3:20 Cavity & Polymorphic
  • 3:59 Overwrite & Multipartite
  • 4:37 Lesson Summary
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Instructor: Beth Hendricks

Beth holds a master's degree in integrated marketing communications, and has worked in journalism and marketing throughout her career.

Computer viruses have evolved from mildly annoying to seriously destructive. In this lesson, you'll learn more about some different types of viruses and how they function in the computer environment.

Computer Viruses

What could be better than receiving an email with the subject line, ''I love you?''' Well, if you were the recipient of such an email in the early 2000s, you might not have been so happy. That's because cybercriminals used the phrase to trick computer users into opening what turned out to be a computer virus.

The ''ILOVEYOU'' virus as it came to be known wrote over users' system and personal files, rendering infected computers essentially useless. At the time, the ''ILOVEYOU'' virus became so widespread that it was one of the most destructive computer viruses to date.

Computer viruses are pieces of malicious computer coding that can be spread from one device to another. They didn't necessarily start out with the intent to damage a computer or steal data, though. Early computer viruses were born more out of curiosity than criminal intent. Today, they are big business for the people behind them - giving them access to confidential data and costing individuals and companies who fall victim millions of dollars.

There are thousands of varieties of computer viruses so it's not possible to create an inclusive list of every virus. But, let's put together a list of the most common types of viruses and how they function.

Common Viruses

Viruses, just like viruses that can enter the human body, take on all sorts of shapes and sizes. Here are some common ones.

Boot Sector, Program, Macro

Boot Sector

The boot sector viruses can overtake your computer when it is booting up. They are not quite as pervasive as they once were (when computers operated more with insertable disks), but they can still be transmitted primarily through removable media, such as a USB or a flash drive.

Program Virus

A program virus is launched when a program is installed or executed. They can also be attached to CDs, removable media, or even email, but instead of infecting a computer at start-up, they go to work when you open a program, even a seemingly innocent one. These are sometimes referred to as ''trojan horse viruses,'' as they are hidden from their unsuspecting victim.


The macro virus disguises itself as coding language in word processing and spreadsheets. It comes along in things like word processing and spreadsheet programs and is written in the same macro language those programs use for their legitimate processes. This virus, embedded in a Microsoft Word document, for example, will cause the program involved to perform a series of unintended actions immediately when the program opens.

Hijacker, Direct Action, Resident


If you've ever logged on to the internet and noticed that your homepage has changed or settings in your browser window have been modified without your permission, you've likely been the victim of a browser hijacker. Often, these are adware or spyware that attach to your computer when you download some type of program from the internet.

Direct Action

One of the most common types of computer viruses, the direct action virus, attaches to .exe and .com files and becomes active once those files are launched. This virus installs to a computer's memory and can infect any number of files - from those near where it's located in the computer to files on an entire computer network at a business. After you execute a file, the virus springs to life.

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