What is a Computer Virus?

Last Updated : 04 May, 2024

A computer virus is a type of malicious software program (“malware“) that, when executed, replicates itself by modifying other computer programs and inserting its code. When this replication succeeds, the affected areas are then said to be “infected“. Viruses can spread to other computers and files when the software or documents they are attached to are transferred from one computer to another using a network, a disk, file-sharing methods, or through infected email attachments.

For Example, if you get an email with a bad attachment and open it by mistake, the virus in the attachment can start infecting your computer. In simple terms, a virus is bad software that gets installed on your computer without you knowing. It attaches itself to another program. When you run the infected program, the virus acts at the same time and can make copies of itself to infect other programs or files. Most computer viruses do mean things like destroying data.

What Does a Computer Virus Do?

A virus can harm or destroy data, slow down system resources, and log keystrokes, among other things. A virus can have unexpected or harmful outcomes during this procedure, such as destroying system software by corrupting data. Some viruses are made to mess things up by deleting files, messing up programs, or even wiping out your hard drive completely. Even if they’re not super harmful, viruses can still slow down your computer a lot, using up memory and making it crash often. Others might just make copies of themselves or send so much stuff over the internet that it’s hard to do anything online.

Virus vs. Malware – What is the difference?

Viruses and malware are often used interchangeably, but they’re not quite the same. Here’s how they differ:

Aspect	Virus	Malware
Definition	A type of malicious software	A broader category of harmful software
Behavior	Self-replicating	Can include viruses, worms, trojans, etc.
Spread	Often requires user interaction	Can spread through various methods, including email, downloads, and vulnerabilities
Damage	Can corrupt or delete files	Can cause a range of harm, including data theft, system damage, and spying
Detection	Can be detected by antivirus software	Requires comprehensive security measures and practices
Examples	Morris Worm, ILOVEYOU	WannaCry ransomware, Zeus trojan

History of Computer Virus

Viruses have been attacking various devices for a long time, spreading through the Internet or other means. They are often created to steal information or completely ruin devices. The first computer virus, called the “Creeper system,” appeared in 1971 as an experimental virus that could copy itself. Following that, in the mid-1970s, the “Rabbit” virus emerged, which replicated very quickly and caused significant damage at the same pace. The virus known as “Elk Cloner” was created in 1982 by Rich Skrenta. It spread through a floppy disk containing a game and attached itself to the Apple II operating system.

The first virus for MS-DOS, called “Brain,” appeared in 1986. It was designed by two Pakistani brothers and overwrote the boot sector of floppy disks, making it impossible for the computer to start. It was originally meant to be a copy protection system. In 1988, more destructive viruses began to surface. Until then, most viruses were considered pranks with funny names and messages. However, in 1988, “The Morris” became the first widely spreading virus.

Different Types of Computer Virus

Each type has a unique way of infecting and damaging computers. Here are a few examples:

Type of Virus	Description
Boot Sector Virus	Attacks the part of the computer that starts up when you turn it on. Boot Sector Virus can also spread through devices like floppy disks. Often called a memory virus.
File Virus	Attaches to the end of a file and modifies how a program starts to run the virus’s code first.
Email Virus	Hides in email messages and activates by clicking a link, opening an attachment, or interacting with the email.
Polymorphic Virus	Changes its form every time it installs to avoid detection by antivirus software.
Macro Virus	Activates by running a program capable of executing macros, often found in documents like spreadsheets.
Multipartite Virus	Infects the computer’s boot sector, memory, and files, making it difficult to detect and remove.
Encrypted Virus	Uses encryption to hide from antivirus software, includes a decryption algorithm to run before executing.
Stealth Virus	Modifies detection code, making it very difficult to detect.
Resident Virus	Saves itself in the computer’s memory and can infect other files even after the original program stops.
Direct Action Virus	Tied to an executable file, it activates when the file is opened but does not delete files or affect system speed; blocks file access.
Browser Hijacker Virus	Changes browser settings without permission, can redirect to malicious sites.

Causes of Computer Viruses

Through the following activities you may get your device infected by the virus :

1. Sharing the data like music, files, and images with each other.

2. If you open a spam email or an attachment in an email that is sent by an unknown person.

2. Downloading the free games, toolbars, media players, etc.

4. Visiting a malicious website.

5. Installing pirated software(s) etc.

Symptoms of Computer Viruses

Computer viruses can really mess up your computer, so it’s important to know if you might have one. Here are some common signs to watch out for:

Performance Issues:

Slowness: Your computer might be much slower than usual, taking longer to start up, open programs, or load files.
Computer Keeps Shutting Down: If your computer keeps crashing, freezing, or showing a blue screen, it could be because of malware messing with your system.

Suspicious Activity:

Unknown programs or files: You might see programs or files on your computer that you don’t remember installing.
Pop-ups and spam: You might get a lot of annoying pop-up windows or spam emails, which could mean malware is trying to control your computer or bombard you with ads.

File and System Changes:

Missing or messed-up files: Important files might disappear or become corrupted, possibly because of malware deleting or changing them.
Changes to security settings: Malware might turn off your firewall or antivirus software to make your computer more vulnerable.

Network Issues:

Weird internet stuff: You might notice big jumps in your internet use or see programs you don’t recognize using the internet.
Trouble connecting: Malware might mess with your internet connection, making it hard to get online or download stuff.

Examples of Viruses in Computer

Virus Name	Description
Morris Worm	One of the first and most widespread computer viruses, the Morris Worm was a self-replicating program that spread across the early Internet in 1988, causing delays and crashes on many devices.
Nimda	Appearing in 2001, Nimda targeted web servers and computers running Microsoft Windows. It spread through various methods, infecting quickly and widely.
ILOVEYOU	In 2000, the ILOVEYOU worm spread through emails disguised as love confessions. It overwrote data and caused extensive damage.
SQL Slammer	This fast-spreading computer worm emerged in 2003, exploiting a vulnerability in Microsoft SQL Server. It caused significant network congestion and disrupted Internet services.
Stuxnet	Developed in 2010, Stuxnet was a sophisticated worm aimed at damaging industrial control systems, particularly Iran’s nuclear facilities. It exploited zero-day vulnerabilities.
CryptoLocker	CryptoLocker, a ransomware Trojan from 2013, infected hundreds of thousands of computers, encrypted victims’ files, and demanded a ransom to unlock them.
Conficker	First detected in 2008, Conficker exploited weaknesses in Windows operating systems, creating a large botnet and causing widespread infections.
Tinba	Discovered in 2012, Tinba is a banking Trojan that primarily targets financial institutions to steal login credentials and banking information.
Shlayer	Since 2018, Shlayer has been a macOS-specific Trojan spreading adware and unwanted programs through fake software updates and downloads.

How To Prevent Your Computer From Viruses?

Here are some important ways to make your computer safer and stop viruses from getting in:

Software Protections:

1. Install a good antivirus program: This is like a guard for your computer. Choose one from a trusted company and make sure it stays up to date with the latest virus fixes.

2. Install anti-malware software: Besides antivirus, consider getting anti-malware too. It can protect you from different kinds of bad stuff.

3. Turn on your firewall: Your firewall acts like a wall, stopping bad stuff from getting in and out of your computer.

4. Keep your software updated: Make sure your computer’s software, like Windows or Mac, your web browser, and other programs, are always updated. This fixes any holes that viruses might use to get in.

How To Remove Computer Viruses?

To remove a computer infection, you can choose from two options:

Do-it-yourself manual approach: This means you try to fix the problem on your own. Usually, you start by searching online for solutions. Then, you might have to do a lot of tasks to clean up your computer. It can take time and might need some experience to finish everything.
Get help from a reliable antivirus product: Another option is to use antivirus software. This software is designed to find and remove viruses from your computer. You just need to install it and let it do its job.

What is Antivirus?

Antivirus software is a program that searches for, detects, prevents, and removes software infections that can harm your computer. Antivirus can also detect and remove other dangerous software such as worms, adware, and other dangers. This software is intended to be used as a preventative measure against cyber dangers, keeping them from entering your computer and causing problems. Antivirus is available for free as well. Anti-virus software that is available for free only provides limited virus protection, whereas premium anti-virus software offers more effective security. For example Avast, Kaspersky, etc.