10 worst computer viruses in history

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It’s not a secret that computer viruses can lead to severe damages.


‘I love You’: a computer virus caused $10 billion in damage and exposed vulnerabilities which remain 20 years on.


ILOVEYOU is considered one of the most virulent computer viruses ever created. This virus infected computers through email and appeared as a love confession to the recipient. Once people clicked on the attachment, it immediately sent itself out to everyone in the user’s email list, overwrote files, and made the infected computer completely unbootable.


It was catastrophic for large corporations and governments. Having spread among roughly 50 million computers in just 10 days, it caused the CIA, Pentagon, and a host of large corporations to shut down their email systems.




Sasser made a lot of problems in 2004, causing $500 million in damage. The fast-spreading computer worm has wreaked more havoc on computer users worldwide, affecting several businesses, banks and government offices, including Britain’s Coastguard.

The creator of the virus, who caused so much damage, was a teenager from Germany. He was quickly arrested after one of his «friends» betrayed the young hacker for a $250,000 bounty on his head from Microsoft.




This virus is not only among the most expensive, but also one of the most widespread on the Internet. In 2001, it caused $635 million in losses. Users of the Windows operating systems reported sluggish machines and computers that quit or rebooted for no reason.




SQL Slammer was a 2003 worm that infected 200,000 computers and incurred $750 million damages. It’s one of the most sophisticated worms on this list.




In 1998, a student from Taiwan created the computer virus Chernobyl (also known as CIH). About 500 thousand personal computers were affected, and losses are estimated at $1 billion. CIH was considered one of the most dangerous viruses, because immediately after activation, it could damage BIOS chip data and destroy all information from hard drives. However, the creator of the virus has never been prosecuted, and now he works at Gigabyte company.




Did you ever get an email with the subject “I send you this file in order to have your advice.”? Congratulations, you know Sircam!


The SirCam computer worm caused more than $1 billion in damage in 2001. In addition to spreading, the virus can delete a victim’s hard drive or fill the remaining free space on the hard drive, making it impossible to save files or print.




Melissa is categorized under Macro virus and enacted as an email worm that hi-jacked around 1 million PCs within a few days of its release. It replicated itself by sending mass mail to the contacts of the infected user. It transmitted through emails with the subject line ‘important message from’ with a document with pornographic sites and replicated itself using outlook to speed up its process.




The Code Red worm came to light in 2001 and invaded about 975,000 hosts.

It announced its presence by shouting “Hacked by Chinese!” in the infected web pages and entirely used the targeted computer’s memory for execution. Unfortunately, it left no trace in the hardware (like files on a hard drive), which complicated the forensic analysis.

The damage ran into 2.4 billion USD.




Conficker, or Downup or Downadup, is a worm of unknown origin for Windows that first showed its ugly face in 2008. This malware proved how dangerous the overabundant security gaps in Windows could become as it exploited them to create a botnet.

9 million systems became hosts to Cornficker in every imaginable country, including places like private businesses, governments, individuals.

Very few worms managed to infect so many computers and do so much damage — $9 billion.




Sobig appeared in 2003 as another worm, just like Mydoom. However, its success as the most dangerous cyber virus is second only to Mydoom’s as it managed to create about $30 billion in worldwide damage. It reached Europe, the US, and Asia. The authors released several Sobig versions quickly known from Sobig.A to Sobig.F. The last one was the worst.

This malware showed itself as a legitimate piece of software attached to emails.

It disrupted the activities of many businesses worldwide, with the Air Canada ticketing being the most famous problem during its time.




The Mydoom outbreak is the worst virus attack ever to happen. Its estimated damage went as high as $38 billion. It also went by the name of “Novarg.” It was a worm that found its way around the internet mass emails. As this worm was active, it was responsible for about a quarter of the world’s email traffic.


As Novarg arrived into a system, it would scan it for fresh addresses. Then it sent copies of itself to those addresses. It also linked the infected computer into a botnet whose purpose was to carry out DDoS (Distributed Denial of Service) attacks. These attacks managed to shut down a website, or a server, by overwhelming it with junk traffic.


The Mydoom author was a wanted man. A quarter-million USD reward was available for his

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