What is a Computer Virus? Causes, Effects, and Proven Prevention Tips

28 September, 2025
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Computers can be infected with some risky viruses that can cause huge data loss. Let’s talk about “What is a Computer Virus?” Several organizations are hiring professionals with skills that can protect computers against online threats.

In the end, we will introduce you to a reputed training institute offering a dedicated training program related to ethical hacking. What are we waiting for? Let’s get straight to the point!

What is a Computer Virus?

A computer virus is a kind of harmful software that attaches itself to other files or programs when it is run. By introducing its own malicious code, it can duplicate itself and spread from one machine to another, much like a biological virus.

Details of What is a Computer Virus?

This may result in a number of negative consequences, including data corruption, system performance lag, or unapproved access to your machine. Let’s take a look at “What is a Computer Virus?”

Different Types of Computer Viruses

S.No.	Types	What?
1.	Boot Sector Virus	Infects a hard drive’s boot sector, often known as the Master Boot Record (MBR), and runs its code each time the computer boots up.
2.	File Infector Virus	Affixes itself to executable files, including those ending in.exe or.com, and becomes active when the user launches the malicious application.
3.	Direct Action Virus	It discovers other files to infect fast, unloads itself from memory, and only activates when an infected file is executed.
4.	Resident Virus	Conceals itself in a computer’s random-access memory (RAM), giving it the ability to infect files and programs that the system opens or runs.
5.	Multipartite Virus	A sophisticated virus that targets both the boot sector and executable files and can infect a computer in several ways.
6.	Polymorphic Virus	An extremely sophisticated virus that is always changing its signature and code to avoid being discovered by antivirus software.
7.	Macro Virus	Composed in a macro language, it propagates by contaminating spreadsheets and documents, usually via email attachments.
8.	Overwrite Virus	Replaces a file’s content with malicious code of its own, rendering the file unusable and erasing the original contents forever.

Key Characteristics of Computer Viruses

The following are some of the key characteristics of computer viruses:

Self-Replication: The ability of a virus to replicate itself and propagate to other files, programs, or systems is one of its basic traits.
Requires a Host: A virus cannot function as a stand-alone application; to propagate and become active, it must affix itself to a valid executable file or document that contains macros.
Dormancy: Many viruses have a latent phase during which they remain hidden within a system until a particular occasion or trigger causes their dangerous code to become active.
Activation Mechanism: In order to execute their payload, viruses frequently employ a “logic bomb” or “triggering” mechanism, which can be a certain time, date, or user activity (such as opening a file).
Malicious Payload: The payload, or the code intended to carry out a malicious operation, is executed by the virus after it has been triggered. This can be anything from showing obnoxious messages to stealing data, corrupting files, or taking over the machine without authorization.
Evasion Techniques: Some viruses utilize sophisticated strategies to evade detection, such as stealth, which involves actively evading antivirus software, or polymorphism, which involves changing their code with each infection.

Common Causes of Computer Viruses

S.No.	Causes	What?
1.	Infected Email Attachments	Viruses may pose as benign files, such as invoices or photographs, and infect your computer as soon as you access them.
2.	Malicious Websites and “Drive-by” Downloads	A virus can be downloaded and installed on your computer automatically without your knowledge or agreement when you visit a compromised website.
3.	Pirated Software and Unofficial Downloads	Unreliable sources frequently combine free or cracked software with malware and hidden viruses.
4.	Infected Removable Media	A virus can enter your computer using an infected memory card, external hard drive, or USB device.
5.	Malicious Advertisements (Malvertising)	An online ad on a trustworthy website may include a hidden virus that infects your computer when you click on it or even just when the page loads.
6.	Software and Operating System Vulnerabilities	Viruses can easily infiltrate your system through outdated software that has unpatched security weaknesses.
7.	Social Engineering	Manipulating individuals into taking activities or disclosing private information, frequently by tricking them into installing a virus without realizing it.

Major Effects of Computer Viruses

The following are the major effects of computer viruses:

Information about major effects of computer viruses

System Performance Degradation: Your computer may operate substantially slower, freeze, or take a long time to start due to viruses using up system resources like CPU and RAM.
Data Corruption and Deletion: Important files may be purposefully or inadvertently corrupted or permanently erased by a virus’s payload, rendering them unusable.
System Instability and Crashes: A virus can make your operating system unstable by interfering with essential system functions, which can result in repeated crashes and the “Blue Screen of Death.”
Unauthorized System Changes: Viruses can install new, undesirable programs without your consent, change the homepage of your web browser, and change your system settings.
Data Theft and Espionage: Viruses linked to spyware are made to steal private data, including credit card numbers and passwords, and transmit it to the attacker.
Network and Email Spamming: A virus can take over your network or email account and use it to transmit harmful links or spam emails to all of your contacts, which will spread the infection.
Loss of Control: An attacker may occasionally be able to remotely access your computer using a virus, giving them the ability to inspect your files and take control of your machine.
System and Application Hijacking: A virus has the ability to take over particular applications, disable your antivirus program, and prevent you from accessing security websites.

Real-World Examples of Famous Computer Viruses

S.No.	Examples	What?
1.	ILOVEYOU (2000)	This virus, also known as the “Love Bug,” was disseminated by email using the subject line “ILOVEYOU.” Millions of people were tricked into opening an attachment that overwrote their files and sent it to everyone in their address book, causing billions of dollars’ worth of harm. It did this by taking advantage of human curiosity and emotion.
2.	Melissa Virus (1999)	Melissa, one of the first well-known macro viruses, infected Microsoft Word documents and propagated over email. Email servers were overloaded and severely disrupted when a user accessed an infected document that would automatically send an email to the first 50 individuals in their contact list.
3.	WannaCry (2017)	Although WannaCry is a well-known example of ransomware, it is technically a worm. It encrypted a victim’s files and demanded a Bitcoin ransom by taking advantage of a flaw in older Windows PCs. It disrupted large institutions like hospitals and global enterprises as it quickly spread throughout more than 150 nations.
4.	Stuxnet (2010)	One famous example of a cyberweapon is Stuxnet. The sophisticated worm was made to specifically target Iran’s nuclear program’s specialized industrial control systems (SCADA). Stuxnet showed that malware might physically harm vital infrastructure in the real world.
5.	Storm Worm (2007)	By posing as a breaking news article about a storm in Europe (“230 dead as storm batters Europe”), this worm employed social engineering. It transformed compromised machines into a “botnet” that criminals could employ for distributed denial-of-service (DDoS) attacks and massive spam campaigns.

How to Prevent Computer Viruses?

You can prevent computer viruses in the following ways:

Install and Maintain Antivirus/ Anti-Malware Software: To guard against emerging dangers, use a reliable security tool and make sure its software and virus definitions are updated on a regular basis.
Keep Your Software and OS Updated: Apply security patches to your operating system and apps on a regular basis to address security flaws that viruses can take advantage of.
Be Cautious with Email Attachments and Links: Never click on dubious links or open unusual attachments, especially if they seem to be from someone you know.
Use a Firewall: By acting as a barrier, a firewall keeps unwanted users from accessing your computer and stops dangerous network traffic.
Practice Safe Web Browsing: Be cautious while using “free” downloads from unofficial sources and only visit reputable, safe websites (check for HTTPS in the URL).
Back Up Your Data Regularly: Make regular, safe backups of your most important files so that, in the case of an attack, you can swiftly restore your data without having to pay a ransom.
Be Wary of Removable Media: Before accessing or running any files from any USB drives, external hard drives, or other removable media, check them for viruses.
Use Strong Passwords and Multi-Factor Authentication (MFA): To provide a crucial extra layer of protection against credential theft, use a different, complicated password for each account and, if at all possible, use multi-factor authentication.

What to Do If Your Computer Gets Infected?

S.No.	Factors	Why?
1.	Disconnect from the Internet	To stop the infection from propagating and from interacting with an attacker, disconnect your computer from the internet and any networks right away.
2.	Restart in Safe Mode	To increase your chances of removing the virus, start your computer in Safe Mode, which stops it from loading and operating.
3.	Run a Full System Scan with Antivirus Software	To find and quarantine or eliminate the malware, run a comprehensive system scan with your updated antivirus program.
4.	Delete Infected Files and Change Passwords	After the scan is finished, change all of your passwords right away, especially for your social media and banking accounts, and remove or quarantine any compromised files.
5.	Restore Data from a Backup	To make sure you have an uninfected copy of your files, restore your system and data from a recent, clean backup if the virus damaged or erased any files.

Conclusion: Staying Safe in the Digital World

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During the training sessions, students will be able to test their knowledge & various tools to find out computer viruses and solve the issue under the supervision of professionals. Moreover, online sessions will facilitate students’ remote learning.

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Frequently Asked Questions

About What is a Computer Virus?

1. What exactly is a computer virus?

A computer virus is a malicious software application that replicates and spreads by attaching itself to other files in an attempt to harm a computer, steal data, or interfere with regular computer operations.

2. How does a computer virus spread?

Computer viruses spread in the following ways:

Infected Email Attachments,
Malicious Downloads,
Infected Removable Media,
Malicious Websites & Ads (Malvertising), and
File Sharing & P2P Networks.

3. What are the main causes of computer viruses?

The following are the main causes of computer viruses:

Infected Email Attachments,
Malicious Downloads,
Infected Removable Media,
Vulnerable Websites & Malicious Ads, and
Outdated Software & Operating Systems.

4. What are the signs that my computer might have a virus?

The following are the signs that your computer might be infected with a virus:

Significant Performance Degradation,
Unusual Pop-ups, Redirects, & Ads,
Files & Applications Behaving Abnormally,
System Instability & Crashes, and
Suspicious Network & Email Activity.

5. What damage can a computer virus do to my system?

A computer virus can do the following damage to your computer:

Data Corruption & Deletion,
System Performance & Instability,
Unauthorized System Changes,
Data Theft & Espionage, and
System & Network Disruption.

6. What are the most common types of computer viruses?

The following are some common types of computer viruses:

File Infector Virus,
Boot Sector Virus,
Macro Virus,
Polymorphic Virus, and
Multipartite Virus.

7. How can I prevent my computer from getting infected?

In the following ways, you can prevent your computer from getting infected:

Install and Maintain Antivirus/ Anti-Malware Software,
Keep All Software & Operating Systems Updated,
Be Cautious with Emails and Downloads,
Use a Firewall, and
Back Up Your Data Regularly.

8. Do I really need antivirus software in 2025?

Because cyber threats have grown more complex and are able to get past the fundamental safeguards provided by operating systems, antivirus software is still necessary in 2025.

9. What should I do immediately if my computer gets a virus?

You should do the following things immediately if your computer gets a virus:

Disconnect from the Internet & Network,
Restart in Safe Mode,
Run a Full System Scan,
Delete Infected Files & Quarantine Threats, and
Change All Passwords.

10. Can free antivirus programs protect me from computer viruses?

Yes, free antivirus software provides a decent foundational level of defense against prevalent viruses and malware, but it frequently lacks the sophisticated capabilities and all-encompassing security of premium options.