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Top 15 Dangerous Computer Viruses in History: How To Protect Your Computer From It?

I am Aabis Ashfaq from Pakistan. I am studying in Pharm-D (Doctor of Pharmacy) at the University of Lahore.

What Is Virus?

In computer science, a digital virus is a computer program that can copy itself and infect a computer without permission or knowledge of the user. In other words, it is malicious software (or "malware"). A virus performs some action on an infected system with malicious intent, such as corrupting data, stealing information, sending spam, or rendering the system inoperable. However, some viruses perform these actions only if certain conditions are met, such as a date has passed since January 1st or a particular button is pressed.

For example, W32/Simile was written to demonstrate the lack of security provided by Microsoft Active Template Library (ATL) Class Wizard in Visual C++ 6.0 for Windows Forms applications which allowed any form created from that wizard to be decorated with the ContextMenu attribute, which would execute any command, script or DLL as long as it was included in the assembly. As a result of this demonstration and subsequent discussion amongst security professionals, Microsoft removed support for ATL Class Wizard from Visual C++ 2008.

Viruses can spread themselves by attaching themselves to other, legitimate programs. They use different infection strategies:

Some viruses can attach themselves to several executables and later execute these files randomly when the infected system is booted up again.

According to many dictionaries, malicious software such as Trojans and computer worms may not be considered viruses because they do not have an independent life cycle. However, the term "computer virus" is also used in common parlance to describe other types of malware, even those that do not have the reproductive characteristics of viruses.

Top 15 Computer Viruses in History

A virus is an infectious form of software that can replicate without being controlled by a host. It can spread from one computer to any other computer it infects and has SAD (Self-Awareness and Self-Replication) capabilities.

There are currently more than 2 million viruses that threaten PCs, laptops, and handheld devices like smartphones, tablets, and iPads. This number seems huge, but we still think there could be many more viruses out there that haven't yet been discovered since this new breed of malware authors is constantly creating new forms of malware with advanced features.

The main factors differentiating legit applications from malicious software tend to be its lack of author attribution or system modification capability.

In this article, we have compiled a list of the top 15 most dangerous viruses in history. It's worth mentioning that at least two particular kinds of viruses were not taken into account since they require physical contact with the victim: biological and chemical viruses.

So here it goes.

15. Tritax / CIH virus (1998)

The first virus to destroy PC BIOS chips

The Tritax or CIH virus was discovered in 1998 by a Vietnamese security researcher Tranx Knghiem. This malware attacked computers equipped with certain IBM compatible PCs containing their unique PC BIOS code and spread through executable boot sector infectors.

Tranx also released an online vaccine that required those infected to download it and burn it to a CD before restarting the computer with this disk in the drive.

The CIH virus was also notable for being the first to destroy PC BIOS chips, rendering them permanently inoperable, which greatly increased its destructive potential.

14. Anna Kournikova (2001)

Infected hundreds of thousands of computers but failed to do any damage.

This infamous malware was known for triggering mass hysteria among office workers when it infected hundreds of thousands of computers around the world in 2001. The hoax started after an email was sent around telling everyone that if they opened certain attached files containing images or video clips -supposedly related to Russian Tennis star Anna Kournikova- they would receive $20,000 in digital cash.

The email was sent from an unknown sender, and the attached files were said to be either a 3GP or MP3 file, which displayed a short movie of Anna Kournikova. The virus authors who wrote this malware gave it the name "AnnaKournikova". After execution, it would try and delete certain system files and display annoying pop-up ads infested with sexual content.

13. Michelangelo (1992)

This virus panicked thousands of computer users when they received an email telling them that their PC needed to be repaired because its faulty startup routine was scheduled for March 6th, forcing many business owners to shut down their computers before this date in fear of a computer breakdown. The March 6th date passed without incident; however, in a few months, a new virus appeared in the wild that exploited the panic created by Michelangelo.

12. Anna Kournikova (1999-2002)

This was one of the fastest-growing viruses ever, infecting tens of millions of PCs worldwide within just a couple of months. However, it didn't cause many problems apart from wasting processing power and slowing down computers when running specific image files. But even with its relatively low threat level, it caused massive disruptions to businesses because most corporate networks shut down every time an infected file was accessed or opened.

11. Good Times (1994)

This virus got its name from a line in the TV show "Mr Bill's Real Life Adventures" where an actor portraying a computer user informs other users that his computer is suffering from a virus called Good Times. The virus would begin by playing this message and then display a graphic of Mr Bill vomiting before overwriting files on the hard drive and corrupting them so they couldn't be opened or reverted to their original state no matter what was tried, causing massive financial losses to the companies affected as well as wasting countless man-hours trying to restore computers after infections occurred.

10. Storm (2007)

This worm quickly infected more than one million computers within just four hours of appearing in the wild and caused $2 billion worth of damages which earned it 9th place on our list. It is considered to be the largest and most costly virus ever recorded. The Storm worm exploited a critical remote code execution vulnerability in Microsoft's Internet Explorer browser to automatically download and install itself onto any computer it could find running Microsoft Windows and then spread itself onto other computers using infected email attachments, peer-to-peer networks, instant messaging services and removable drives such as USB flash drives.

9. Chernobyl (1999)

This destructive virus was named after the Ukrainian city where the nuclear meltdown that created its source code occurred in 1986. The main thing about this virus that separates it from others is that it deletes files instead of just corrupting them as traditional viruses do by changing data so programs can't read it properly or in some cases where the damage is so severe that files can't be opened or reverted to their original state. The virus was written by a 16-year-old teenager and spread rapidly through email spam after its release in 1999, infecting tens of millions of PCs worldwide within just days.

8. ILOVEYOU (2000)

This worm remained undetected for over ten years. It silently replicated itself throughout millions of Windows computers worldwide before finally being discovered during an investigation into another computer worm called SoBig, which used the ILOVEYOU exploit to replicate itself on systems infected with this virus. It caused more than 10 billion dollars worth of damages worldwide before security researchers found a way to stop it from spreading. It worked by sending itself out to everyone in the victim's Windows Address Book and then spreading by emailing copies of itself using various file formats that included .jpg image files.

7. Zeus (2004)

This virus is the first major banking Trojan, allowing criminals to control infected computers remotely without their owner's knowledge. Zeus works by intercepting sensitive information such as login credentials when an infected user visits a website for online banking or making other financial transactions. That means any bank account details entered are passed back to criminals complete with username, password, expiration date and security question answers which allows them to bypass standard authentication procedures so they can log in directly at will and have their criminal activity go undetected until its too late.

6. Stuxnet (2010)

This worm was first discovered in July of 2010 when an engineer at Iran's main uranium enrichment plant sent an urgent email to the International Atomic Energy Association reporting that thousands of centrifuges used for enriching Uranium were spinning out of control. Security researchers believe this worm is one of the most advanced ever used for cyber warfare. It was designed specifically for sabotage and targeted critical infrastructures such as power plants, not traditional computers or home PCs. It successfully compromised Iranian nuclear facilities by targeting Windows systems running Siemens industrial software and hardware, which enabled it to cause physical destruction to machinery contained within them without being detected.

5. ExploreZip (1991)

Commonly known as "WildList", this virus was first released as a trial version of a compression program that would later become WinZip. This is the first virus to use polymorphism, which altered its file characteristics every time it spread so it couldn't be detected by traditional anti-virus software designed to recognize viruses based on their unique signatures, which remained unchanged from one infection to another. It also used stealth tactics such as encrypting itself with a simple XOR encryption algorithm and hiding its code in the Windows System directory where no other file could be placed due to operating system limitations at the time.

4. CIH (1998)

Also known as the "Chernobyl Virus", this virus is believed to have been created by a 17-year-old high school student from Ohio. CIH spread rapidly through removable devices such as floppy disks and caused so much damage worldwide that Symantec, the main distributor of anti-virus software at the time, set up a website to help victims clean their computers free of charge because most companies didn't yet have protection in place. It was also one of the first viruses to infect non-Windows systems when it spread to Macs using infected .exe files copied from PCs. The virus caused permanent damage to LCDs because it disabled pixel shader hardware in graphics cards which allowed users to see the entire contents of system memory on their screens along with any data being processed or transferred by them, which can cause severe damage if someone is looking over your shoulder when this happens because it's very easy for them to see all the information you are working with including passwords and private messages sent over instant messaging.

3. Melissa (1999)

Also known as "The Ugly Email-Worm", this virus was the first widespread worm to use email addresses harvested off infected computers as its primary means of proliferation, which spread like wildfire across the globe by sending itself out to everyone listed in Windows Address Book on an infected PC with no subject line or any message text included in the email which caused many users not even using Microsoft software at that time to open it because there was no way for them to know it was an executable file. The author intentionally used a VERY common female name 'Melissa' when creating the malware's code. If anyone found it, they would assume it was just another regular email from a regular person and not bother to read it or take any precautions before activating it. This is the first virus to use something called 'payload', which involves the virus doing everything it's supposed to do as assigned by its creator, such as replicating its code, spreading itself and causing whatever damage its author has designed it to cause on an infected system once triggered such as encrypting files or performing some other type of permanent destructive action that cannot be reversed through conventional means such as formatting your hard drive and reinstalling Windows like most infections.

2. Stuxnet (2010)

Also known as "The Mother Of All Viruses", this worm targeted specific types of machinery used in industrial settings such as power plants and factories by targeting the Windows operating systems running them. This virus is believed to have been created by a nation-state because of its ability to spread so far across an entire network. The worm's payload includes over 5 million lines of code, which was largely unheard of before this infection came on the scene. The combination of attacking Windows machines and SCADA software used for remote monitoring of industrial control systems made Stuxnet one of the most dangerous pieces of malware ever released into our global community. What made Stuxnet even more unique is its multiple methods for spreading its destructive payload, including USB drives, network drives, external hard drives, and any other removable media connected to infected PCs.

1. The Internet (1969)

We all take the Internet for granted now. Still, this communications protocol was created as a way to enable any PC from around the world could talk with other computers by first connecting to a central mainframe somewhere which would link you up with whatever computer or server you needed to connect with, there were no servers back then only mainframes. The Internet creators never intended it to be used as a means for spreading viruses and malware because they didn't even know what those were at that time because nobody had yet thought of using computers to spread malicious code. In 1969, the only thing an infected PC could do was turn on its monitor and display whatever text anyone wanted it too which meant if someone wrote a virus in those days, it would be very benign and only display text. Today, the Internet is used for email, instant messaging, social networking, online banking, and everything else involving data moving across networks, making it the perfect medium for viruses to do their damage.

10 Tips to Protect Your Computer From Viruses and Malware

1. Keep Your Antivirus Software Updated

Most antivirus software detects viruses based on simple file signatures. A lot of times, when new viruses are produced, they do not have any unique files signatures, which means the antivirus software cannot detect them immediately! Therefore you need to keep your antivirus software updated to stay up to date with the latest viruses and how to detect them.

2. Only Download Programs from Reliable Websites

You should download programs like Adobe Flash Player or VLC Media Player directly from their official websites (i.e., For example, suppose you try to download a pirated copy of Adobe flash player from a random website instead of getting it from Adobe itself. In that case, there is a high chance that you will get some malware installed on your computer when you install the pirated version, even though it looks legitimate!

3. Do Not Click On Suspicious Popup Messages

Most web browsers these days automatically block popup messages that appear on new web pages. However, if you get a popup message and want to know more about what it's offering, don't click on it! Google search for more information about the popup message by typing: "removed popup text" in the Google search bar, and you might be able to find out why your computer is displaying such a message. Or better yet, close all of your browsers and re-open them instead of clicking on suspicious-looking popups.

4. Do Not Click On Suspicious Email Attachments

This one is very important! If you do not know who sent you an email attachment, then never open it! You should also watch for file types like .exe, .vbs, .scr, and .bat because most viruses are sent through email as attachments you can unknowingly download. If you need to open an attachment, make sure it is not attached with a file type listed above!

5. Use Antivirus Software On All of Your Devices

This might seem like common sense, but many people forget about their cell phones! Most antivirus software works on PCs and Macs, but it may take some time before they release a version for your smartphone/tablet because Apple locks down the iOS so much. I would recommend getting antivirus from companies such as Kaspersky or Dr Web, which have made applications for iOS and Android systems. That way, you can install antivirus on all of your devices and make sure they are safe from viruses or malware.

6. Do Not Click On Suspicious YouTube Videos

Many reports have been about people getting viruses and malware installed on their computers by simply visiting YouTube and clicking on a link that leads to a virus! If you want to watch a video, you should go to the official website such as instead of watching the video through an embedded player.

7. Keep Your Software Updated

You should always keep your software updated because most companies release patches that fix security issues with their programs very frequently! For example, Adobe releases every month, which fix known security issues with their software. Software updates usually fix security issues that hackers are always trying to exploit to get into your computer.

8. Only Install Applications From Official Stores

You should only install applications from official stores such as the Apple App Store or the Google Play store! Most of the time, people download pirated versions of popular programs from third-party websites, including malware inside them. Hence, if you want to get a program, you shouldn't search for one outside of an official store because it can put your computer at high risk.

9. Turn Off AutoRun For Removable Drives And Media

If you have removable drives inserted into your computer, I would recommend turning off 'AutoRun' because if you do not, every time you plug in a USB drive, CD, or DVD, it can automatically install malware onto your computer. If you are not inserting any removable drives into your computer, there is no need to turn off AutoRun.

10. Use Strong Passwords

You should always use strong passwords which contain upper and lower case letters, special symbols, numbers and are at least ten characters long! For example, "afasfas3552#$" would be considered a strong password, whereas "monkey1" or "ABC123!" would be considered weak. Most people think that just having numbers in their password makes it secure. Still, hackers can easily figure out your password by finding out your birthday, address, or other details about you, so always try to make sure your passwords are at least ten characters long and include symbols!

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2021 Muhammad Aabis Ashfaq

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