Top 10 Most Disastrous Computer Viruses Ever


Computer viruses and worms cause billions of dollars in damage each year worldwide. Companies invest a huge amount of money to safe-guard, maintain and service their servers and systems from viruses and malware. There are millions of viruses in the world with risk levels from minimal to critical. Computer viruses like Stuxnet, ILOVEYOU and Sobig F are some of the world’s most dangerous and disastrous computer viruses ever created. Damages caused by such dangerous computer viruses are determined by the loss to the Information Technology world in terms of dollars. Which are the most disastrous computer viruses in history?

Let’s check out the list of top ten most disastrous computer viruses in history (viruses and worms):

10. SQL Slammer

SQL Slammer Worm

SQL Slammer is a computer worm that infected 75,000 victims within ten minutes. The worm caused havoc by causing denial of service on some Internet hosts and also slowed down general Internet traffic. Michael Bacarella is the first person to alert the general public about the worm. The worm got its name as “SQL Slammer” by Christopher J. Rouland, the CTO of ISS. Although titled “SQL slammer worm”, the program did not use the SQL language. A proof of concept code demonstrated at the Black Hat Briefings by David Litchfield led to the invention of the worm.

9. CIH

CIH Computer Virus Chernobyl or Spacefiller

CIH is the acronym of its founder Chen Ing-hau (a student then at Tatung University in Taiwan). CIH is also known as Chernobyl or Spacefiller. CIH is a Microsoft Windows 9x computer virus which first emerged in 1998. The destructive virus infected 60 million computers internationally, resulting in an estimated $1 billion US dollars in commercial damages. The payload of the virus is highly destructive to vulnerable systems, overwriting critical information on infected system drives, and in some cases destroying the system BIOS. The name “Chernobyl Virus” refers to the complete coincidence of the payload trigger date in some variants of the virus and the Chernobyl accident, which happened in the Ukrainian SSR on April 26, 1986. The name “Spacefiller” refers to the capabilities of the virus to find gaps in the existing program code and write its own code in-between.

8. Code Red

Code Red Computer Virus

Code Red is a dangerous computer worm that infected 359,000 hosts in July 2001. The worm infected computers running Microsoft’s IIS web server. The Code Red worm was first discovered and researched by eEye Digital Security employees Marc Maiffret and Ryan Permeh. The employees named it “Code Red” because Code Red Mountain Dew was what they were drinking at the time. The worm spread itself using a common type of vulnerability known as a buffer overflow.

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7. Conficker

Conficker Virus

Conficker is a computer worm that infected millions of computers including government, business and home computers in over 190 countries, making it the largest known computer worm infection since the 2003 Welchia. Conficker virus is also known as Downup, Downadup and Kido. The virus primarily targets the Microsoft Windows operating system. The computer worm was first detected in November 2008. This worm originally targeted users of social networking websites like Facebook, Skype, Yahoo Messenger, and email services such as GMail, Yahoo Mail, and AOL Mail. Even today, millions of computers still get infected by this awful computer virus. Conficker infects anywhere from 9 to 15 million Microsoft server systems running everything from Windows 2000 to the Windows 7 Beta.

6. Melissa

Melissa Virus

Melissa is a mass-mailing macro virus. Melissa virus is also known as “Mailissa”, “Kwyjibo”, or “Kwejeebo”. The highly vulnerable Melissa had infected up to 20% of computers worldwide. Melissa is one of the worst computer viruses of all time. Though, this virus doesn’t destroy any computer resources or files but has the potential to cripple the mail servers. The virus is a fast-spreading macro virus which is shared as an attachment in the mail. When opened, the virus can disable safeguards in the host computer. If the virus is opened from a software such as Outlook, it can trigger mails to the first 50 email addresses in the address book.

5. Sasser

Sasser Virus

Sasser is a computer worm that targets computers running vulnerable versions of the Microsoft operating systems Windows XP and Windows 2000. An 18-year-old German computer science student Sven Jaschan from Rotenburg, Lower Saxony is responsible for creating Sasser. On 7 May 2004, the student was arrested for writing the worm. Microsoft offered a bounty of US$250,000 to arrest the coder of the virus. Many companies such as Nordic insurance company, British Coastguard, Delta Air Lines and Goldman Sachs came to a complete halt for few hours due to the worm. The worm caused millions of dollars in loss all over the world.

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4. Sobig F

Sobig F Virus

Sobig is a computer worm, widely spread in its “Sobig.F” variant. The worm infected millions of Internet-connected, Microsoft Windows computers in August 2003. Sobig is not only a computer worm, but also a Trojan horse and sometimes a malware. Sobig appears as an email with an attachment. Sobig has high replicating capabilities and its “Sobig.F” variant set a record in sheer volume of e-mails. On September 10, 2003 the worm deactivated itself automatically. On November 5, 2003 Microsoft announced that they will pay $250,000 for information leading to the arrest of the creator of the Sobig worm. Till date, the creator of the worm has never been caught.

3. Mydoom

Mydoom Virus

Mydoom worm is the fastest spreading e-mail worm ever. The worm set the record surpassing records set by Sobig worm and ILOVEYOU. The worm primarily affects computers running the Microsoft Windows. Many security firms believe that the worm is created in Russia. The actual developer of the worm is still unknown. Craig Schmugar, an employee of computer security firm McAfee named the virus as “Mydoom”. Craig Schmugar is one of the earliest discoverers of the worm. On Feb, 2004, an estimate determined that one million computers are infected with Mydoom virus. Mydoom virus is used by e-mail spammers to send junk e-mail through infected computers.



ILOVEYOU virus is a computer worm that attacked tens of millions of Windows personal computers worldwide. ILOVEYOU worm is sometimes referred to as Love Letter. The virus has its origin from Philippines. On and after 4 May 2000, the virus spread e-mail messages with the subject line “ILOVEYOU” and the attachment “LOVE-LETTER-FOR-YOU.txt.vbs”. The disastrous computer virus infected the PC by overwriting random types of files. The virus caused US$5.5–8.7 billion in damages worldwide and an estimated cost of US$15 billion to remove the worm. On May 5, 2000 the virus started to infect computers in Hong Kong, Europe and United States. 50 million infections within ten days led many companies shut their mail servers to protect themselves from the infection. ILOVEYOU virus infection is one of the world’s most dangerous computer related disasters.

1. Stuxnet (most disastrous computer virus)

Stuxnet Virus (variants of most disastrous computer viruses)

Stuxnet is the most dangerous and disastrous computer virus in the world. The Stuxnet virus is far more dangerous than the cyber-weapon one can imagine. According to few sources, the virus was designed jointly by the U.S. and Israeli government specifically to attack the Bushehr nuclear power plant in Iran. Neither of the states has confirmed this. The virus damaged roughly a fifth of Iran’s nuclear centrifuges by causing them to spin out of control. In mid-June 2010, a security company VirusBlokAda identified the worm. The most affected countries include Iran, Indonesia and India. According to experts, the development of Stuxnet is the largest and costliest development effort in malware history.