What is a Computer Virus? - Definition, Types & Protection

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  • 0:01 Definition of a Computer Virus
  • 1:07 How the Virus Spreads
  • 1:55 Types
  • 2:18 How to Protect Against
  • 4:24 Lesson Summary
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Lesson Transcript
Instructor: Monica Gragg

Monica has taught college-level courses in Tourism, HR and Adult Education. She has a Master's in Education and is three years into a PhD.

In this lesson, we'll discover the nature of computer viruses and how they are commonly spread. We'll look at the types of viruses, protection schemes, and some real-life examples.

Definition of a Computer Virus

On March 26, 1999, millions of people around the world opened an email they thought was from a friend or colleague. The subject line read, 'important message.' The email was one short sentence suggesting there was a private document for the viewer's eyes only. It sounded serious, but there was a smiley face at the end of the message. When millions of people clicked on the document, a virus called Melissa, named after an erotic dancer in Florida, infected their computer. The virus reached into their computer and stole 50 email addresses to which to send the same message. This is what we call a computer virus.

Computer viruses spread enormously because they are asymptomatic. In other words, they are difficult to detect. You see, a computer virus, also known as a worm, is an unwanted malicious program designed to cause damage to computers on a large scale. So, if a virus looks like a normal email attachment, greeting card, or funny image, people are likely to click on it, and the virus spreads. Beware. . . computer viruses also come in the form of audio, video, and even anti-virus programs!

How the Virus Spreads

The virus can cause damage in many forms. A mild version, like the Melissa virus, can spam other email addresses and social media accounts. Other worms can spread into your computer to delete files, erase hard disks, cause malfunction, and steal private information. Let's look at a more serious virus.

Have you heard of ILOVEYOU, born a year after the Melissa virus? Like Melissa, The ILOVEYOU malware program came in the form of an email attachment. Instead of stealing 50 email addresses, ILOVEYOU stole all of your email addresses. It deleted your images saved as jpeg or jpg and corrupted your music files. It also controlled your Internet browser to make you click on other viruses and shared your passwords. It is estimated that the ILOVEYOU virus caused billions of dollars worth of damages.


There are different types of computer viruses with different techniques. Let's take a look at a few of them:

  • Trojan viruses are downloaded and spread other malicious programs and can remotely control the computer it is downloaded on.
  • Botnets put infected computers into a network where they can be remotely controlled.
  • Scareware uses a disguise to infect a person's computer. It usually looks like a safe anti-virus program.

How to Protect Against

As technology advances, so do hackers. In some cases, hackers outgrow security measures. It's nearly impossible to prevent computer viruses, but there are things you can do to protect yourself. Viruses like Melissa and ILOVEYOU are very common now, making them easier to detect. If you receive a suspicious email, don't open it or download the attachment. They are usually found in your junk folder anyway, so instead of deleting them, report them as spam.

Internet browsers are set up to be very convenient for us. We save our passwords, bank details, and other personal information for 1-click purchases and quick access to frequently visited sites. While it's convenient for us, it's also convenient for hackers. Every few months, you should clear your Internet cache and browsing history. This will also allow you to update your passwords. I know the process sounds tedious, but the time spent speaking with your bank about fraudulent charges is even worse.

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