Cyber Plague: 6 Most Infamous Computer Viruses In History

Last updated on December 13th, 2024 at 11:53 am

Computer viruses are one of the most destructive threats to modern society. Every day, cybercriminals are making new, dangerous codes in hopes that they can infect as many computers as possible.

If you fail to protect yourself from computer viruses, you can face consequences such as massive financial damages and identity theft.

In this article, you will learn about the most infamous computer viruses that shut down the entire world.

A computer virus is a destructive program that’s used to perform malicious activity. Viruses work by attaching to other applications, replicating themselves, and then spreading to other devices, impacting the way your computer performs.

Computer viruses can cause damage such as stealing personal data and corrupting your operating system. It can even steal sensitive information such as your bank account credentials and your PII (Personal Identifying Information).

Without further ado, you’ll now find out about the most infamous viruses in computer history:

In May 2000, a young hacker from the Philippines made an email worm that would turn out to be one of the most destructive viruses ever created. This virus would send computer users a strange love letter with the subject line “ILOVEYOU”.

A user will then curiously open the email and click the attached file called “LOVE-LETTER-FOR-YOU.TXT.VBS”, activating the virus. The virus will then release a devastating payload that corrupts important system files, crashes the computer, and sends copies of itself to all the contacts in the user’s address book.

ILOVEYOU quickly spread throughout the world and caused billions of dollars in damages. In addition, caused many computer users to experience panic and confusion. Even after the virus was patched by Microsoft a month later, the ILOVEYOU virus serves as an alarming example of how much chaos a computer virus can cause when no one is aware of the risk it poses.

Introduced in 2001, Klez has become famously known as one of the most lethal viruses in history, infecting 7.2% of the world’s computers. This mass-mailing virus took advantage of a known vulnerability that was found in Microsoft Outlook e-mail programs at the time.

Klez worked by sending infected emails to random addresses using a fake address. Once the user opens the email’s attachment, Klez will then start up its e-mail engine and send itself to other e-mail addresses that are found on the user’s computer. A year later, several variants such as Klez. H appeared.

The Klez virus was transmitted to over 206 countries, and infected millions of PCs. Unlike ILOVEYOU, this virus continued to spread for many years, resulting in financial damages costing tens of billions of dollars.

Known as the fastest-spreading malware in computer history, MyDoom is a computer worm that infects PCs by spreading itself through mass emailing. The damage of MyDoom was so significant that it accounted for 25% of all emails sent worldwide, leaving a lasting impact on the cybersecurity landscape.

In 2004, many computer users received a strange email that said “I’m just doing my job, nothing personal, sorry.” Once the user opens the attachment, MyDoom will enter into the Windows operating system. The virus will then spread to other email addresses in the victim’s computer, and send new copies of the virus.

What made MyDoom worse than ILOVEYOU and Klez is that it will use the infected computers as a botnet to launch DDoS (Distributed Denial Of Service) attacks. These cyberattacks were intended to shut down the SCO Group and Microsoft websites. Despite being created over 20 years ago, MyDoom is still used today to infect computers with poor malware protection. No one has ever found out who the developer behind this computer worm was, or why they created it in the first place.

First detected in 2007, Zeus is a computer trojan that’s used for stealing financial data. Often called Zbot, this virus became one of the most widespread botnet Trojans in the world, affecting millions of computers worldwide.

The Zeus Trojan works by sending phishing emails to targeted computer users. Once the user downloads the malware inside the email, the PC will communicate with other infected computers and join a botnet. The hacker will then control these corrupted machines like a maestro in an orchestra, and use the botnet to steal massive amounts of banking credentials through keylogging.

The Zeus Trojan caused over 3 billion dollars in damages, and in 2011, the source code of Zeus was leaked. Even though Zeus is not as popular as it once was, its source code was used to create other botnet viruses.

The Zeus source code leak led to hacking groups creating different variants such as GameOver Zeus. This variant contained all the features of the original Zeus, but could also deliver the ransomware named CryptoLocker.

Once a computer user installs GameOver Zeus, the user’s PC will join a Zeus botnet and trigger CryptoLocker ransomware. CryptoLocker will locate all the file types in the operating system and then encrypt it. The ransomware will then display a red ransom note saying “Your important files encryption produced on this computer.” The only way a victim was able to gain access to their PC again was if they paid a hefty ransom.

This ransomware became famously known for how quickly it spread, and how difficult it was to break its asymmetric encryption. In 2014, researchers were able to release a free encryption tool that allowed victims of CryptoLocker to decrypt their files again. Unfortunately, different variants of CryptoLocker still exist today.

This famous 2017 ransomware affected hundreds of thousands of computers and held them hostage. Many companies were impacted by WannaCry, and it caused major disruptions in essential healthcare and emergency services.

Also known as EternalBlue, WannaCry worked by taking advantage of a security flaw that was found on outdated Windows operating systems. Just like the CryptoLocker ransomware, WannaCry used encryption to lock users out of their PCs. If the victim wasn’t able to pay the ransom that the hackers demanded, the files on the computer would be permanently deleted.

The WannaCry ransomware attacked computers across 150 countries, and many of the victims included Nissan, FedEx, Hitachi, Telefonica, and more. WannaCry stopped spreading once a UK security researcher was able to develop a kill switch to disable the ransomware. Additionally, French researchers found a way to decrypt affected computers without paying a ransom.

While the terms malware and virus are often used interchangeably, they are technically not the same. Malware is a general term that’s used to describe all types of malicious software.

Computer viruses are a type of malware that’s similar to biological viruses. Just as a person who is infected with the flu can affect other nearby people, computer viruses can spread infected code to other non-infected devices.

Viruses can be shared through emails, flash drives, and websites, and they can attach themselves to legitimate programs and files. A computer user can unexpectedly activate a computer virus by opening an infected application. Once this happens, the virus may turn off system functions, delete important files, and modify other files and programs.

There are many different types of malware. These are the most common examples:

• Worms – These programs can replicate itself and spread over a computer network. Unlike viruses, a worm spreads through email attachments masquerading as a legitimate file or by taking advantage of a vulnerability in a targeted computer system.
• Trojans – This malware can camouflage into legitimate files to infiltrate into your computer. To learn more about how they work, read the article What Is A Trojan Attack? How You Can Avoid Them.
• Ransomware – This malicious program prevents users from accessing their machines until they make a ransom payment, just as the name implies. Similar to worms, ransomware can spread across a network and encrypt computer servers, which can paralyze an entire company.
• Spyware – This is a type of malware that enters a user’s computer, gathers personal data, and sends it to third parties without the user’s consent. Cybercriminals may use spyware to steal, track, and sell sensitive information such as usernames and passwords that are used to access credit cards and bank accounts.
• Rootkits – This malware allows a hacker to gain administrative access to a computer without being detected. To find out how rootkits can do this, read the article What Are Rootkits? How To Detect & Prevent Them.
• Fileless Malware – This malicious software uses legitimate programs, such as Microsoft Word, to infect a user’s computer. These malicious programs don’t use executable files like traditional malware, which makes them difficult to detect and remove.

It is important to remain vigilant and practice good security habits to avoid being a victim of computer viruses. Check that your programs and OS stay up-to-date to avoid any vulnerabilities that viruses can take advantage of. When you are browsing the web, pay close attention to the URLs that are showing in your address bar.

Carefully inspect your inbound emails to avoid any potential phishing attacks, especially if you’re not sure who the sender is. Be on guard of any files you download, and make sure those files come from trusted sources.

If you notice strange slowdowns on your PC, don’t ignore them. If you think something suspicious is happening, there’s a chance your instinct is correct.

When a virus has infected your computer, the most proven way to remove it and restore it to its initial state is to run a rootkit scan with a high-quality antivirus.

Bitdefender Total Security is the most top-rated antivirus software you can get. It repeatedly gives excellent results at independent lab tests, is cheaper than some of its competitors, and comes with useful security features.

Bitdefender offers broad protection against online threats, starting with antivirus, firewall, and ransomware. It also safeguards against brute force attacks, malicious links, and dangerous attachments.

MalwareBytes Premium offers AI-powered protection and plenty of excellent security features that can help you shield your devices from many malware threats. It provides ransomware protection, web protection, phishing protection, rootkit protection, and more.

With a simple and easy-to-use interface, you can secure all of your devices without compromising speed. It also includes robust scam protection, so you can easily shut down robocalls and phishing attempts.

ESET Home Security provides fast, lightweight malware protection for your devices. It comes with 24/7 real-time protection against viruses, trojans, worms, and spyware, so you can have peace of mind. With Ransomware Shield, you can stop malware that tries to lock you out of your data to demand a ransom payment.

This antivirus includes safe banking and browsing protection, so you can safeguard your online activities from keyloggers and other online threats. ESET Home Security is easy to use and allows you to share your protection with family and friends with the free ESET HOME management platform.

Acronis True Image offers reliable cyber protection software for your entire home. Boost your computer’s security with impressive real-time cyber protection against ransomware, crypto mining, and viruses. With Identity Protection, you can safeguard your personal information from identity theft.

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Concerned About Your Privacy Online? Read The Article Should I Use a VPN? Find Out Why VPNs Are Important