Types of Computer Viruses and How to Prevent Them

Computer viruses can be very destructive they can cause a loss of information and cost a lot of money to repair, in this article I am going to look at the types of computer viruses and how to prevent them.

What is a Computer virus?

A computer virus is a software program or piece of code that can copy itself and infect a computer without user knowledge.

This results in the computer’s performance being reduced, as the virus uses some of its resources.

An example of this would be a virus going through your email contacts, then sending itself to those people as an email you were copied on, without your knowledge.

What was the first Computer virus?

Computer viruses are a major nuisance for computer users. Viruses cause the data on computers to be corrupted, lock them up completely or allow an unauthorized user to take control of it.

In 1986, Fred Cohen wrote a program called a “virus” and introduced the world of computing to this new type of software code. However, many people don’t know what the very first computer virus was.

What was the name of the first computer virus?

The first computer virus is called “Creeper”. It was short-lived since it only replicated itself onto other computers running the same flawed software.

Creeper wasn’t destructive either; all it did was display a message on whatever machine is infected. Although Creeper didn’t cause any damage, it opened the door to malicious viruses such as “The Reaper” and “Trin00”.

The first computer virus (that wasn’t such a novelty) was called “Brain”. This virus appeared on UNIX-based mainframes around 1986.

The brain had no special tricks or capabilities. It only moved from one UNIX machine’s account to another.

After that, it simply overwrote the victim’s login program with itself every time the user would boot up their computer.

Many people regard the first destructive computer virus as PE (portable executable) infector for MS-DOS (which was also known by two other names: Lehigh, or 1633).

PE infector was compiled on July 18, 1986, by Rich Skrenta. It had two routine “mutations”; it could delete .exe files and place itself in .com files.

What is the worst computer virus of all time?

The Creeper virus was created in 1971 by Bob Thomas at BBN. The “War Games” movie had recently come out, and the character of David Lightman (played by Matthew Broderick) inspired him to create it.

The idea came from a challenge where someone asked if they could create a virus that automatically sent a counter to 1 each time it infected a new machine.

The Creeper virus was designed to show that this could be done and illustrate the capabilities of such a program.

The original code did not cause any damage, and merely displayed or printed “I’m the creeper: catch me if you can!” on the user’s screen every time the machine was booted.

The intent was to create a virus that simply spread itself around and counted the number of computers infected, but ended up getting out into the wild.

Shortly after, there was another program created that copied the source code of Creeper but added a line so it would delete all files in the current directory when executed.

This version was called “The Reaper” and was much more destructive. The Creeper source code has since been lost, but the Reaper is still used to this day in software development as an example of how not to write code.

Bit flip virus is a computer virus that flips arbitrary bits in the hardware of infected computers. It overwrites data or program instructions by changing single bits in the machine code of executables.

The name is derived from bit rot, a gradual degradation in the accuracy of data stored in computer memory due to physical decay of the individual memory locations and also in connection with cosmic radiation or other environmental effects that can induce such decay; after enough time has passed, certain critical bits in affected memory locations may be flipped from 0 to 1, or the reverse.

In a bit flip attack on a computer, however, these arbitrary changes occur not randomly but at specific points in executable code.

By changing binary data such as program instructions to completely different data, the virus creates software that does something else than intended by its creator.

The usual result is that the program destroys data on the computer, prints threatening messages and/or reports to a third party (such as a crime boss), or otherwise disrupts normal operations.

What are the different types of computer viruses?

There are many categories of computer viruses, simply because there are many types of malicious software out there.

Viruses can be written in almost any programming language (such as Visual Basic or C++) and will often exploit a security vulnerability that allows them to gain access to your system. The majority of viruses will contain several different “features,” such as:

Boot Sector Viruses

These types of viruses infect the boot record or master boot record (MBR), which allows them to get executed before anything else on your computer boots up.

Once they infect this part of your system, they can modify certain parts of the boot process, such as the partition table or master boot record.

This is one of the most common types of viruses, though they are less dangerous than other viruses because they can be removed once you have booted into Windows.

File Infector Viruses

The file infector virus attaches itself to specific executable files to infect your system. Once your computer is infected, the virus will change the executable file so that when you attempt to open it, or run it, for example for opening a .exe file on Windows systems, the virus runs first.

Macro Viruses

A macro virus is a type of computer virus that attaches itself to documents created in different applications.

For example, a Word document with macros enabled or an Excel spreadsheet that contains macros can be infected by macro viruses.

Script Viruses

Script viruses are written in languages that are used to “control” the way your computer works, such as JavaScript and VBScript.

These types of viruses will infect other files on your computer, which can open up the possibility of it infecting other computers on a network.


Worms are different from viruses in that they do not need to attach themselves to another file to be executed.

They are completely self-contained and will attempt to gain access to as many systems as possible. Once they have infected one system, they will travel from computer to computer using networks and communication protocols.

Worms are similar to viruses in that once a system becomes infected, it will need to be cleaned or reinstalled.

Trojan Horses

A Trojan horse is one of the most dangerous types of virus because it appears as normal, beneficial software.

For example, you may see an email that claims to be from your bank with a link or attachment called “updates” but when you click on the link or open the attachment it will infect your computer.


A spyware virus is created with the intent of collecting information about you, your computer usage, and perhaps even about your friends.

For example, spyware can be used to monitor the websites that you go to or the time that you spend on specific activities online.

Spyware can also track information such as which programs are being run on your system, where you are logging onto the internet from, what people are saying in chat rooms, which websites you visit, and other information.


Adware is a virus that is created with the intent of showing you advertisements when your computer is infected.

The ads will appear on your web browser or may even be “injected” to show up when you are typing something in a search engine.


Rootkits are one of the most dangerous types of viruses. Once your computer is infected with a rootkit, other types of malware can be loaded onto your system and given the same permissions as other parts of your operating system.

How to prevent viruses?

There are several different ways that you can increase the security of your computer. Using antivirus software is one way to prevent viruses.

Antivirus software will periodically scan your system for any virus, adware, spyware, or other malware that has made it onto your computer.

Another way to protect yourself from viruses is by using anti-malware software like Malwarebytes.

Malwarebytes will scan your system for the same types of malware that antivirus software would, but it allows you to run scans on-demand instead of having to schedule them in advance with another program. It is also free while many other antivirus programs are not!

Something else you can do to prevent viruses is by only downloading files from trusted sources.

Even if you know the file is safe, other people may have downloaded it and infected it with a virus without knowing, which could make your system infected when you download that specific file.

You should also only install software from trusted sources. While this may sound very similar to what was mentioned above, you should also keep in mind that every time you visit a website running Adobe Flash or another plugin, there is a potential for it to be infected with malicious code.

If you download and install this software from a trusted source, the chances of getting the program contaminated will be much lower than if you were to download it from an unknown source.

A final way to prevent viruses is by using anti-spam and anti-phishing software. Anti-phishing software will look for suspicious emails that try and trick you into clicking on a link or opening an attachment, then it will block that email from ever reaching your inbox again.


In this article, we covered the different types of computer viruses and how to prevent them, hopefully, you learned something from this, thank you for reading.

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