Our internet-connected world is plagued by computer viruses, that were once a laughing matter. Every day, more than 350,000 new pieces of malware are discovered, costing over £55 billion annually. However, there is one virus that leads the pack with £38 billion in damages: The Mydoom virus in 2004.(That we currently know of at least)
In this article, the most destructive PC or laptop viruses are ranked according to their financial impact.
However, these malicious programs are just the tip of the iceberg.
The viruses in this article are just a few of the millions of malware apps that attack consumers and businesses every year.
>>>Related Post: The Best Way To Remove A Computer Virus<<<
10 of the worst computer viruses of all time
In the list of the 10 most famous computer viruses below, we show the costs, dates, reach, and other key facts.
First, a note about terms: we use the words “virus” and “worm” interchangeably because most readers search for them that way.
But there’s a subtle difference that we explain after the list (Just being honest as always).
1. £38 billion for Mydoom
In 2004, Mydoom caused an estimated £38 billion in damage, but its inflation-adjusted cost is actually £52.2 billion.
In technical terms, Mydoom is a “worm” that spreads through mass emailing. Mydoom accounted for 25% of all emails sent at one point.
After scraping addresses from infected computers, Mydoom sent copies of itself to those addresses.
As part of the attack, these infected machines were incorporated into a botnet, which was used to launch distributed denial of service (DDoS) attacks on other computers.
A target website or server was intended to be shut down by these attacks.
Today, Mydoom generates 1% of all phishing emails.
With 3.4 billion phishing emails sent every day, that’s no small feat. Since its creation 16 years ago, Mydoom has infected enough poorly-protected PC’s to send 1.2 billion copies of itself per year.
The developer of this dangerous computer worm was never caught, despite a £250,000 reward being offered.
2. £30 billion for Sobig
It turns out that the 2003 Sobig computer virus is actually another worm. In terms of scope, it is second only to the Mydoom virus.
The £30 billion figure includes Canada, the U.K., the U.S., mainland Europe, and Asia. Sobig, then the latter SobigF the most damaging version of the worm, were released in quick succession.
Cybercriminals used this program to masquerade as legitimate computer software attached to emails.
Air Canada’s ticketing system was disrupted, and countless other businesses were affected.
The creator of the successful bug was never caught, in spite of its widespread damage.
3. £19.8 billion for Klez
Klez ranks third on the list of the worst computer viruses ever created.
In 2001, it infected about 7.2% of all computers, or 7 million PCs, causing about £20 billion in damages.
In addition to sending fake emails, the Klez worm attempted to deactivate other viruses.
Klez was released in several variants, like other viruses and worms. The virus infected files, copied itself, and spread throughout each victim’s network. Over the years, it evolved into more destructive versions.
Since most of the computer viruses on this list first appeared on the web, Windows has come a long way. Thanks to Microsoft Defender, you’re always protected.
4. £15 billion for ILOVEYOU
It worked by sending a fake “love letter” that looked like a harmless text file.
As with Mydoom, this attacker sent copies of itself to every email address in the infected machine’s contacts.
More than 10 million PCs had been infected by the virus shortly after its release.
Onel de Guzman, a college student from the Philippines, created the virus.
He wrote the virus to steal passwords so he could log into free online services he wanted to use.
According to reports, he had no idea how far his creation would spread. Loveletter is another name for this virus.
5. The WannaCry attack cost £4 billion
WannaCry is ransomware (We previously wrote about this here), a virus that locks up your computer (or cloud files) and holds them hostage.
Businesses, hospitals, and government agencies that failed to pay the WannaCry ransomware had to rebuild their systems from scratch.
200,000 computers worldwide were infected with the malware.
A 22-year-old security researcher from the UK discovered a way to disable it.
Particularly vulnerable were computers with out-of-date operating systems.
That’s why security experts always recommend updating your systems regularly.
Once again, ransomware strikes
Universal Health Services was hit by one of the largest computer virus attacks in medical history in September 2020.
A U.S. hospital chain with more than 400 locations was reportedly hit by ransomware.
Healthcare workers were forced to switch to paper records after the attack forced surgeries to be cancelled.
6. £3 billion for Zeus
A computer virus called Zeus hit the web in 2007. It is a tool for online theft.
Three years later, Unisys estimated that it was responsible for 44% of all banking malware attacks.
It had breached 88% of Fortune 500 companies, 2,500 organizations, and 76,000 computers in 196 countries by then.
In Eastern Europe, the Zeus botnet was used to transfer money to secret bank accounts by taking over computers for a remote “bot master.”
In 2010, more than 100 members of the crime ring were arrested, mostly in the U.S. Some of the virus’ source code survives in newer botnet viruses and worms.
There is documented damage to £100 million caused by Zeus.
It is undoubtedly much higher in terms of lost productivity, removal, and undocumented theft. In today’s pounds, this virus is estimated to cost £3.7 billion, adjusted for inflation.
7. £2.4 billion for Code Red
In 2002 the code red computer virus infected 975,000 hosts.
The virus displayed the message “Hacked by Chinese!” on infected web pages, and it ran entirely in memory on each machine.
Most of the time, it didn’t leave a trace on hard drives or other storage devices.
The financial costs are estimated at £2.4 billion.
The virus attacked the White House’s website, causing a distributed denial of service (DDoS) attack.
To defend against Code Red, the White House had to change its IP address.
8. Slammer gets £1,2 billion
An estimated £750 million was lost by 200,000 computer users in 2003 due to the SQL Slammer worm.
Randomly selecting IP addresses, this computer virus exploits vulnerabilities and spreads to other computers.
Through these victim machines, a DDoS attack was launched on several internet hosts, significantly slowing internet traffic.
U.S. and Canadian banks were especially hard hit by the Slammer worm, which took ATMs offline in many locations.
Imperial Bank of Commerce customers in Toronto were unable to access their funds.
Using IP addresses in Ukraine, China, and Mexico, the attack resurfaced in 2016.
9. £665 million – CryptoLocker
Since their 2017 peak, ransomware attacks like the 2013 CryptoLocker virus have declined.
The malware encrypts files on upwards of 250,000 machines. Users were informed that “your important files have been encrypted on this computer.” A payment window accompanied the ransom note.
CryptoLocker was made and sent using the Gameover Zeus botnet by its creators.
Sophos reports that the average ransomware attack costs a business £133,000. CryptoLocker cost £665 million if 5,000 companies were affected.
10. £500 million – Sasser
Sven Jaschan, a 17-year-old German computer science student, wrote the Sasser worm.
The laptop or computer virus’ creator was arrested at the age of 18 after a £250,000 bounty was posted.
According to Jaschan’s friend, he also wrote the damaging Netsky.AC attack as well as the Sasser worm.
When it was discovered Jaschan was a minor when he wrote the malware, he was given a suspended sentence.
Millions of PCs were affected by the Sasser worm, and while some reports estimate damages at £18 billion, a more likely figure is £500 million.
Here are some other notable viruses
A gargantuan digital iceberg lies beneath the top 10 worst computer viruses above.
We may miss the forest for a few outstanding trees, with a million new malware programs popping up every three years. Viruses that have wreaked havoc over the years include:
- Mimail: This worm used infected machines to launch DDoS attacks, but it was relatively easy to remove.
- Yaha: Another worm that has several variants, thought to be the result of a cyber-war between India and Pakistan
- Written in C++, the Swen computer worm disguised itself to look like a 2003 OS update. Its financial cost has been pegged at £10.4 billion, but not reliably.
- Storm Worm: This worm attacked millions of computers in 2007 by sending an email about approaching bad weather.
- Tanatos/Bugbear: A keylogger virus that infected 150 countries in 2002.
- Sircam: 2001 computer worm that sent counterfeit emails with the subject line or similar to, “ Attached is a file to which I would like your advice.”
- Explorezip: The worm spread across thousands of local networks using fake emails.
- In 1999, Melissa was the most dangerous computer virus. It sent copies of itself that looked like NSFW pictures. U.S. FBI estimates cleanup and repair costs at £80 million.
- Flashback: Over 600,000 Macs were infected by Flashback in 2012, including Apple’s Cupertino headquarters. Best Tip: Macs now have more malware than PCs in 2020.
- Conficker: The 2009 virus still infects many legacy systems and can cause significant damage if activated.
- Stuxnet: According to reports, this worm destroyed Iranian nuclear centrifuges by sending damaging instructions.
Worms vs. viruses
A virus is different from a worm in that it requires another program to run, such as a word processor or web browser.
Worms, on the other hand, are self-contained and can run, copy, and send copies of themselves independently.
Worms are some of the most dangerous computer viruses for this reason.
The best way to tell if you have a virus
Virus detection is easy today. View the latest antivirus report by opening your computer’s antivirus software.
Windows 11 comes with built-in virus protection called Windows Security.
You can find it by typing “Windows Security” into your PC’s search bar. To view your latest scan, click the shield icon on the left.
The methodology
We estimated lost productivity, duration of infection, and approximate numbers of infected machines to find the worst computer viruses in the world.
Estimates of virus, malware removal and repair costs were also used.
The cost of computer viruses is not tracked by any government or international organization.
The majority of computer virus cost estimates you’ll find online come from a single source.
In 2003, a UK security firm called mi2g published a very short (2-paragraph) article. In most cases, the figures in that article seem inflated, especially after our independent research.
By cross-checking these estimates against data from government agencies and security analysts combined with our 25 plus years in cybersecurity, we adjusted them up or down.
In a nutshell
It is estimated that computer viruses cost £55 billion each year in cleanup and repair costs.
In 2004, the Mydoom virus caused an estimated £38 billion in damages. Other notable worms include the Sobig worm, which cost £30 billion, and the Klez worm, which cost £19.8 billion.
Thanks to today’s secure PCs and operating systems, viruses and worms have a much harder time to infect, however, it doesnt mean we are all safe unfortunately.
>>>Related Post: The Best Way To Remove A Computer Virus<<<
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