Top 10 Most Damaging Computer Virus in History.

Most Damaging Computer Virus

Computer viruses used to be a funny joke, but now they cause serious problems and cost a lot of money. Every day, more than 350,000 new viruses are created and they cost over $55 billion each year. The most damaging computer virus so far was the Mydoom virus in 2004, which caused $38 billion in damages. This article lists the most harmful viruses by how much money they caused in damage. But remember, these viruses are only a few examples of the many damaging computer virus out there, and there are millions of new viruses every year.

What Is a Computer Virus?

A computer virus is a harmful program that sneaks into your device and takes control of it, changing how it works. It often pretends to be a safe program or file and can stay hidden until you open the program it’s attached to.

Once activated, the virus can do things like collect your personal information, block you from accessing files or programs, or spread it to other devices on the same network. You can protect yourself from viruses by using antivirus software, which can stop most harmful programs from infecting your computer.

How is Computer Virus harmful?

A computer virus works by infiltrating a device, often by disguising itself as a legitimate program or document and then altering the way the device operates. Once the virus is activated, it can do many harmful things, such as gathering sensitive information, restricting access to files and programs, and even taking control of the device itself. Some viruses are designed to spread to other devices on the same network, causing even more damage.

How do we protect the device against viruses?

There are several ways to protect your device against viruses:

  1.  Install antivirus software: A good antivirus program can detect and remove viruses from your device.
  2.  Keep your software up to date: Keeping your operating system and other software up to date helps to patch vulnerabilities that viruses may exploit.
  3.  Be cautious of email attachments: Do not open attachments from unknown sources, especially if they are executable files.
  4.  Use strong passwords: Strong passwords that are difficult to guess can prevent hackers from gaining access to your device.
  5.  Back up your files: Regularly backing up your important files can help you recover them in case of a virus attack.
  6.  Avoid suspicious websites: Avoid visiting suspicious websites or downloading files from them as they may contain viruses.
  7. Use a firewall: A firewall can block unauthorized access to your device and prevent viruses from spreading.

By following these steps, you can reduce the risk of your device being infected by a virus.

10 Most Damaging computer virus in history

This article has a list of the Most Damaging Computer Viruses, and it shares their cost, date, and how far they spread. We want to note that we use the words “virus” and “worm” interchangeably, even though they are a bit different.

1. ILOVEYOU – $15 billion

ILOVEYOU – $15 Billion

ILOVEYOU, also known as the Love Bug, was a computer worm that originated in the Philippines in May 2000. It was distributed via an email attachment that appeared to be a love confession from a secret admirer.

  • After being activated, the worm would proceed to replace existing files, extract confidential passwords, and distribute duplicates of itself to every individual listed in the victim’s email contact list, all without their knowledge or consent. The worm spread rapidly, infecting millions of computers worldwide within a few hours. The total damage caused by the worm was estimated to be around $15 billion, making it one of the most expensive computer viruses in history.

2. Mydoom – $38 billion

2. Mydoom – 38 Billion

MyDoom is a computer worm that spread through email in 2004 and caused a lot of damage.

  •  It is considered to be one of the fastest-spreading email worms ever, affecting millions of computers around the world.

  •  MyDoom allowed hackers to take control of infected computers and use them for malicious purposes like sending spam emails or launching cyber attacks.

  •  The worm caused an estimated $38 billion in damages, making it one of the most costly viruses in history. Its origin and creator remain unknown.

3.Sobig – $37 billion

Sobig – $37 Billion

SoBig was a computer worm that first appeared in August 2003 and quickly spread through email attachments, causing an estimated $37 billion in damages.

  • It is known for clogging email servers and slowing down internet traffic due to its ability to send itself to every email address in a victim’s address book.

  •  The worm was also capable of opening a backdoor on infected systems, allowing attackers to remotely control and use the infected devices for malicious purposes.

4. Klez – $19.8 billion

Klez – $19.8 Billion

Klez is a computer worm that first appeared in 2001 and is considered one of the most damaging computer virus of all time. It is estimated to have caused $19.8 billion in damages, with its most significant impact felt in the United States and China.

  •  Klez spread through email attachments, and its payload included the ability to log keystrokes, disable antivirus software, and steal sensitive information from infected computers. The worm could spoof email addresses, making it difficult to trace the source of infection.
  •  The Klez worm was designed to replicate itself and spread to as many computers as possible, which it did successfully, infecting millions of machines worldwide. It was also known for its ability to mutate and change its code, making it challenging for antivirus software to detect and remove.
  •  To protect against the Klez worm, computer users were advised to keep their antivirus software updated and avoid opening email attachments from unknown or suspicious sources. In addition, email servers were configured to block executable files and limit the size of email attachments.
  •  Today, the Klez worm is no longer a significant threat, thanks to improvements in antivirus software and email security measures. However, it serves as a reminder of the importance of computer security and the potential damage that can be caused by malicious software.

5.WannaCry – $4 billion

WannaCry – $4 Billion

WannaCry was a type of ransomware attack that caused widespread damage in 2017, infecting more than 200,000 computers in 150 countries.

  •  It was able to spread rapidly due to a vulnerability in older versions of Windows operating systems.

  •  The attack demanded payment in Bitcoin in exchange for the release of encrypted files, and it caused an estimated $4 billion in damages.

6. Code Red $2.4 billion

Code Red $2.4 Billion

Code Red was a computer worm that infected Microsoft IIS web servers running on Windows NT and 2000 operating systems in 2001.

  •  It spread rapidly, exploiting a vulnerability in the software, and caused significant damage to businesses and organizations around the world.

  •  The worm was designed to launch distributed denial-of-service (DDoS) attacks, effectively shutting down websites and disrupting internet traffic.

  •  It’s estimated that the total cost of damages caused by the Code Red worm was around $2.6 billion, making it one of the most expensive computer viruses in history.

7. Melissa

7. Melissa

Melissa was a macro virus that was spread through infected email attachments in 1999.

  •  It caused widespread disruption by rapidly infecting computers and clogging email servers, resulting in an estimated $1.2 billion in damages.

  •  The virus was named after an exotic dancer in Florida, and it was created by a programmer who was later sentenced to 20 months in federal prison.

  •  The Melissa virus served as a wake-up call to the potential harm of computer viruses and led to increased awareness and preventative measures to protect against them.

8.Sasser $500 million

Sasser $500 Million

Sasser was able to spread rapidly and caused significant disruption to computer networks worldwide.

  •  It caused significant damage, estimated at $1.1 billion. The worm was designed to scan for and infect vulnerable systems, causing them to crash or experience other issues.

  •  It affected millions of computers worldwide before a security patch was released to address the vulnerability.

9. Nimda


Nimda was a computer worm that caused significant damaging computer virus in 2001. It spread through email and web servers, infecting computers and causing disruptions to businesses and individuals.

  •   One of the reasons Nimda was so effective was that it had multiple means of propagation. It could spread through email, infecting computers when users opened infected attachments or clicked on links in the email. It could also spread through web servers, infecting computers that visited compromised websites.
  •    Once a computer was infected, Nimda could replicate itself, spreading to other computers on the network. It could also carry out a range of malicious actions, such as modifying files, deleting data, and creating backdoors for hackers to exploit.
  •    The damage caused by Nimda was significant, with some estimates suggesting that it cost $635 million in damages. Businesses and individuals faced significant disruptions, and many struggled to recover from the attack.
  •    Fortunately, the impact of Nimda was eventually mitigated through the efforts of security experts and software vendors.
  •     However, the incident served as a wake-up call for many organizations, highlighting the importance of strong cybersecurity practices and the need to remain vigilant against emerging threats.

10.SQL Slammer -

SQL Slammer

SQL Slammer was a computer worm that caused significant damage in 2003. It targeted Microsoft SQL Server and Desktop Engine databases, infecting computers and causing widespread disruption.

  •  One of the reasons SQL Slammer was so effective was that it exploited a vulnerability in Microsoft SQL Server and Desktop Engine databases. The worm was able to spread rapidly, infecting large numbers of computers in a matter of minutes.

  •  Once a computer was infected, SQL Slammer could cause a range of issues, including crashing the computer, slowing down network traffic, and causing systems to become unresponsive. The worm was particularly damaging for businesses, as it caused significant disruptions to operations and resulted in lost revenue.

  •  The damage caused by SQL Slammer was estimated to be around $500 million. Businesses and individuals were left struggling to recover from the attack, which highlighted the importance of strong cybersecurity practices and the need for regular software updates.

  •  The incident also served as a reminder of the importance of keeping software up-to-date and regularly applying security patches. Software vendors and security experts worked together to mitigate the impact of the worm and to prevent similar incidents from occurring in the future.

  •  Overall, SQL Slammer was a significant event in the history of cybersecurity, and it remains an important reminder of the importance of taking proactive measures to protect against emerging threats.

Additional notable viruses

In addition to the top 10 damaging computer virus, there have been many other viruses that have caused significant damage over the years. Mimail was a worm that tried to harvest data from infected machines to launch DDoS attacks. It was relatively easy to remove. The Yaha worm, first detected in 2002, was designed to spread via email and targeted machines running Microsoft Windows operating system, causing damage and disruption to infected systems.

  •  Swen was written in C++ and disguised itself as a 2003 OS update. Its financial cost has been estimated at $10.4 billion, but this figure is not reliable.
  •  The Storm Worm, which showed up in 2007, attacked millions of computers with an email about approaching bad weather.
  •  The Tanatos/Bugbear virus, also known as the “I-Worm.Tanatos” virus, was a malicious program that first emerged in 2002, spreading via email and targeting vulnerable Microsoft Windows systems. It caused significant damage to infected computers and networks, and had the ability to steal sensitive information such as passwords and financial data.
  •  In 2001, a computer worm called Sircam propagated through falsified emails bearing the subject line, “I send you this file to have your advice.” Explorezip used fake emails to spread to every machine on thousands of local networks.
  •  Melissa was the most dangerous computer virus in 1999, sending copies of itself that looked like NSFW pics. The U.S. FBI calculated cleanup and repair charges at $80 million.
  •  Flashback was a Mac-only virus that infected over 600,000 Macs in 2012, even infecting Apple’s home base in Cupertino, California. In 2020, there is no more malware on Macs than on PCs.
  •  Conficker, a notorious worm that targeted Microsoft Windows operating systems, has been infecting computers since 2008 and remains a threat to this day due to its ability to evolve and adapt to new security measures.
  • Stuxnet is reported to have destroyed Iranian nuclear centrifuges by sending damaging instructions.

Given the prevalence of malware and the constant evolution of threats, it’s more important than ever to harden your company’s cybersecurity profile. There are many ways to improve corporate cybersecurity, including regular software updates, employee training, and the implementation of strong security protocols.

How We Can Check If Our Device Has A Virus?​

If you suspect that your computer may be infected with a virus, some common signs to look out for include slow performance, frequent crashes, unusual pop-ups or error messages, and If you notice alterations to your system settings or modifications to your files that you cannot account for, it may be an indication of unauthorized tampering.

Nowadays, it’s simple to check if your computer has a virus. You can open your antivirus software and look at the latest report. If you have a Windows 10 computer, it comes with built-in virus protection called Windows Security. To find it, just type “Windows Security” in the search bar and click on the shield icon to see the latest scan.

If you do have a virus, don’t worry – you can follow our guide on how to get rid of it. To add extra protection to your computer, McAfee® uses advanced technology like a deep threat intelligence network and machine learning to detect, protect, and fix issues from the cloud.


To determine the damaging computer virus, we had to rely on estimates of lost productivity, infection duration, and the number of affected computers. We also looked at the cost of repairing the damage caused by these viruses. Unfortunately, there is no central authority that tracks the cost of computer viruses.

Some articles online that claim to list the cost of computer viruses rely on a single source – a brief article by a UK security firm in 2003. We couldn’t find any data to support these estimates, so we adjusted them based on information from various government agencies and security analysts.


Computer viruses are expensive to deal with and cost an estimated $55 billion every year in repair and cleanup costs. The Mydoom virus is considered the most costly computer virus, causing $38 billion in damages in 2004. The Sobig and Klez worms were also very costly, causing $30 billion and $19.8 billion in damages, respectively. Fortunately, modern PCs and operating systems are much more secure, making it difficult for viruses and worms to infect our computers and cause damage.

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