15 Most Dangerous Computer Viruses in the World

15 Most Dangerous Computer Viruses in the World

15 Most Dangerous Computer Viruses in the World

 Viruses and malware on computers will continue to evolve over time, they can become more dangerous, making it very difficult to keep our data protected. The following are the 15 most dangerous computer viruses in the world and new malware threats in 2020 that you need to know about.



Let's start the list of the most dangerous computer viruses in the world with the ILOVEYOU virus which is considered one of the most vicious computer viruses ever created. This was proven by successfully destroying damage to computer systems around the world with a loss of around $ 10 billion. 10% of computers in the world are believed to have been infected. So governments and large corporations took their mail delivery systems offline to prevent infection.

This virus was created by two Filipino programmers, Reonel Ramones and Onel de Guzman. They use social engineering techniques to get people to click on attachments. But the attachment was actually a script acting as a TXT file, because Windows at the time hid the actual file extension. Once clicked, it will send itself to everyone in the user's email and proceed to overwrite files with itself, rendering the computer unbootable.

A Philippine court said the evidence against Mr Guzman was insufficient to support the charges brought against him, as there are no laws against malware. This led to the enactment of the E-Commerce Act to address the issue.

2. Code Red

CodeRed Virus

Another of the most dangerous computer viruses in the world is Code Red which first appeared in 2001 and was discovered by two employees of eEye Digital Security. The virus was given the name Code Red because the pair were drinking Code Red Mountain Dew at the time of its discovery. The worm targeted computers with the Microsoft IIS web server, exploiting a buffer overflow problem in the system.

It leaves very little footprint on the hard disk as it is able to run entirely on memory, with a size of 3,569 bytes. Once infected, it will proceed to make a hundred copies of itself but due to a bug in the programming, it will duplicate many more and end up consuming a lot of system resources.

It will then launch a denial of service attack on multiple IP addresses, notable among them the attack on the White House website. It also allows backdoor access to the server, allowing for remote access to the machine.

This virus sends quite a unique message to the victim's site that is left on the affected web page, “Hacked By Chinese!” , which made it a meme. A patch was later released that was estimated to cause $2 billion in lost productivity. As many as 1-2 million servers were affected and an incredible estimate was that there were 6 million IIS servers at that time.

3. Morris Worm

Morris Worm

Morris Worm or "Great Worm", which is believed to be the pioneer among computer worms distributed over the internet. Conceived to highlight security flaws in Unix systems, its founder Robert Morris, made a fatal mistake that turned a worm from potentially harmless software into a denial-of-service (DDoS) attack machine.

The worm is supposed to ask if there is already a copy running on the computer but instead it just makes copies of itself, slowing down the system. Eventually, it causes crashes and renders the computer completely useless. It is believed that the Morris Worm infected around 6,000 major Unix machines, causing up to $10 million in damage.

4. Nimda

Nimda Virus

Worms, viruses, and Trojan horses all sound pretty scary. But it was actually a computer virus known as Nimda (admin spelled backwards) that hit the internet back in 2001. Within an hour of its release, Nimda hit the top spot of all reported attacks. No wonder, because the worm uses five different transmission routes.

While its primary target is Internet servers running Windows NT and 2000, Nimda also affects ordinary user PCs running Windows. The latter helps it spread quickly and cause major network outages.

5. SQL Slammer

SQL Slammer

The outage at Seattle's 911 service, the collapse of Bank of America's ATM service, and the cancellation of several Continental Airlines flights – these are just a few examples of what SQL Slammer is capable of. This triggered 05:30 UTC on January 25, 2003, infecting its first server. Once that job was done, the Slammer spread rapidly, doubling the number of victims every few seconds, and just ten minutes after it was released in the wild, the number of infected computers grew to 75,000.

The Slammer dramatically slowed internet traffic worldwide, took down several critical systems, caused massive panic and over a billion dollars in damage. The funny thing is, this cybersecurity breach could easily have been prevented. The worm exploits a bug in Microsoft SQL Server. However, the patch preventing it was released six months before the attack, but many organizations either ignored it or didn't apply it in time.

6. Stuxnet

Stuxnet Worm

It is believed to have been created by the Israel Defense Forces in conjunction with the American Government. Stuxnet is an example of a virus created for cyber warfare purposes, as it is intended to disrupt Iran's nuclear efforts.

Computer worms are designed to attack industrial Programmable Logic Controllers (PLC), which allow automation of processes in machinery. Stuxnet is spread by USB thumb drives and targeted software controlling facilities in Iran that have uranium.

The virus was so effective that it caused their centrifuges to self-destruct, making Iran's nuclear development return and costing a lot of money. But eventually Siemens found a way to remove the malware from their software.

7. CryptoLocker

CryptoLocker Ransomware

CryptoLocker Ransomware was released in September 2013 and spreads via email attachments and encrypts users' files so they cannot access them. Once they open the infected email attachment, it will encrypt all personal files on the computer. Even if the virus has been removed, the files will still be encrypted, and therefore inaccessible.

Users will then be extorted by the program, told they need to pay a certain amount of money or Bitcoins, the equivalent of several hundred dollars, to obtain a key to decrypt the files. In addition, a deadline of about a few days was given. If payment is not accepted the key will be destroyed, leaving the user's files completely inaccessible.

About 2% of victims are believed to have paid the ransom. Some of them regained access to their files, while others did not, losing huge amounts of data. The creators are believed to have made tens of millions of dollars from this ransom.

8. Melissa

Melissa Virus

This virus was created by David L. Smith in 1999. It started as an infected Word document and claimed to be a list of passwords for adult websites. This got people curious and when it's downloaded and opened, it will trigger the macro in it and release the payload.

This virus will send itself to the top 50 people in a user's email address book and this causes an increase in email traffic, disrupting government and corporate email services. It also occasionally corrupts documents by inserting Simpsons references into them.

Smith was finally caught when they traced a Word document to him. The file was uploaded using a stolen AOL account and with their help, law enforcement was able to catch it less than a week after this virus started. He cooperated with the FBI in arresting other virus authors, notable among whom was virus creator Anna Kournikova. For his cooperation, he only served 20 months and paid a $5000 fine out of a 10 year sentence. The virus reportedly caused an $80 million loss.

9. MY Doom

MY Doom Virus

Surfing in 2004, Mydoom was a worm for Windows that became one of the fastest spreading email worms since ILOVEYOU. The author is unknown and it is believed the creator was paid to make it as it contains the text message, “andy; I'm just doing my job, nothing personal, sorry.” It was named by McAfee employee Craig Schmugar, one of the people who originally discovered it. 'mydom' was a line of text in program code (my domain) and sensed this would be huge, added 'doom' to it.

The worm spreads itself by appearing as an email transmission error and containing its own attachments. Once executed, it sends itself to an email address in the user's address book and copies itself to the P2P program folder to propagate itself through that network.

The payload itself is twofold: the first opens a backdoor to allow remote access and the second launches a denial of service attack on the controversial SCO Group. It is believed that the worm was created to interfere with SCO due to ownership conflicts of some of the Linux code. This caused an estimated $38.5 billion in losses and the worm is still active in some form today.

10. Sasser

Sasser Virus

The Windows worm was first discovered in 2004 by computer science student Sven Jaschan, who also created the Netsky worm. While the payload itself can be seen as just annoying (it slows down and crashes the computer, while making it hard to reset), the effect is hugely annoying, with millions of computers being infected, and critical, critical infrastructure affected.

The worm took advantage of a buffer overflow vulnerability in the Local Security Authority Subsystem Service (LSASS), which controls the security policies of local accounts, causing crashes to computers. It will also use system resources to spread itself to other machines over the Internet and infect others automatically.

The effect of the virus was widespread when the exploit was patched, many computers had not been updated. This led to over a million infections , taking out critical infrastructure, such as airlines, news agencies, public transport, hospitals, public transport, etc. In all, the damage is estimated to have cost $18 billion. Jaschen was tried as a minor and received a suspended sentence of 21 months.

11. Zeus

Zeus Virus

Zeus is a Trojan horse created to infect Windows computers so that they will perform various criminal tasks. The most common of these tasks are usually man-in-the-browser keylogging and form grabbing. Most computers get infected through drive-by downloads or phishing scams.

First identified in 2009, it has successfully compromised thousands of FTP accounts and computers of large multinational corporations and banks such as Amazon, Oracle, Bank of America, Cisco, etc. Zeus botnet controllers use it to steal login credentials of social networks, email and banking accounts.

It is estimated that more than 1 million computers are infected. The entire operation was sophisticated, involving people from all over the world to act as money mules to smuggle and transfer cash to leaders in Eastern Europe.

About $70 million was stolen and 100 people were arrested in connection with the operation. In late 2010, the creator of Zeus announced his retirement but many experts believe this to be wrong.

12. Conficker

Conficker Virus

Also known as Downup or Downadup. Conficker is a worm whose creator is unknown. This worm first appeared in 2008. Its name comes from the English word, configure. It infects computers using weaknesses in the OS to create botnets.

This malware can infect more than 9 million computers worldwide, affecting governments, businesses and individuals. It was one of the largest known worm infections ever to appear causing an estimated $9 billion in losses.

This worm works by exploiting a network service vulnerability that exists and is not available in Windows. Once infected, the worm resets account lockout policies, blocks access to Windows update and antivirus sites, turns off certain services and locks user accounts.

Then, he started installing software that would turn computers into botnets and scareware to scam users of money. Microsoft then provided fixes and patches with many antivirus vendors providing updates to address this worm.

13. Tinba

Get Virus

Tinba is the pet name for the Tiny Banker Trojan that made headlines in 2016. As the name suggests, its primary target is financial institution websites. Tinba uses man-in-the-browser attacks and network sniffing to obtain user banking information. Account numbers, usernames, passwords, credit card numbers and PIN codes. Everything was stolen and then hacked into bank accounts. Tinba has infected dozens of banking institutions, including giants such as Wells Fargo, TD Bank, Bank of America, Chase, PNC and HSBC.

Its success lies in its small size (20KB) and the way it is spread. Clicking on pop-up websites, downloading software from unreliable sources, or simply opening infected links can lead to infection with Tinba. What's worse, it hides in your system and stays silent until you open the required website.

If you don't want to fall for cyberthreats like this, always check that the banking website you are about to enter has a secure HTTPS connection (all banking websites should use one) and don't enter your sensitive information.

14. Welchia

Welchia Virus

Viruses can also be created to serve ethical purposes. Welchia or Nachi worm is one of them. It is designed to combat and kill the Blaster worm on the user's PC (if any), and prevent further Blaster infection by downloading and installing security patches from Microsoft. After the work was done, Welchia went down by herself.

However, it has a weak point, ethical viruses slow down the computer. As a result, Welchia caused a nine-hour delay in the processing and issuance of visas by the US Department of State. It also consumed three-quarters of the Navy-Corps' capacity, rendering it useless for some time.

15. Shlayer

Shlayer Virus

The operating system most infected with computer viruses is Windows. But that does not mean other operating systems are not likely to be infected with viruses. This is all proven by Trojan Shlayer. It was responsible for around 30% of all macOS attacks in 2019, making it the number one Mac malware threat that year.

Shlayer masquerades as an update for Adobe Flash Player (hence the name comes from). When launched, it runs a series of shell scripts to proliferate various adware or potentially unwanted applications. In most cases, users get Shlayer virus when visiting untrustworthy Torrent websites, clicking on advertisements or downloading files.

The adware-type apps they install deliver intrusive ads that can redirect you to dangerous websites and more hidden downloads. In turn, this can lead to high-risk system infections and disruptions to the Mac operating system.

How to Protect Computer From Viruses?

After you know the list of the most dangerous computer viruses in the world, then how do you protect a computer from these deadly viruses? Actually every day a lot of malicious software is created. No one knows when the next deadly virus will arrive, but what you should know is to always be prepared to prevent it.

The best computer virus removal tools, anti-virus and firewall software are your best protection. Most importantly, always be vigilant when opening files, links, and emails that you don't know where the source is. Since systems are usually difficult to crash, most viruses rely on the weakest link in the chain, namely the person sitting in front of the screen.

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That's all for the article 15 Most Dangerous Computer Viruses in the World. Look forward to other interesting articles and don't forget to share this article with your friends. Thank you…

Also, read the article about 17 Ways to Overcome Slow Internet on Windows 10. And see you in another article. Bye
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