5 worst computer virus in the world of all time

worst computer virus

Computer Virus is any kind of programmable code that’s designed to do harm and spread itself to more computer. These are created by malicious programmers who might want to use your computer to attack  other targets, or might want to steal  your personal information. They might also want to be trying how far there virus will spread.

Different viruses can affect Windows, Mac or Linux computers, and even the data servers that keep companies and even  the internet itself running.

Over the years there have been thousands of viruses spread online and they’ve caused billions of dollars of damage from lost productivity, wasted resources and broken machine. A few dozen of those viruses stand out, some affected specially quickly or affected a lot of people and created a ton of damage all by themselves. Some did all the above.

Since lot of viruses were very bad in a lot of different ways, it’s hard to pick out which one were objectively the worst computer virus. But with that in mind, here are 5 of those extra destructive and worst computer virus of all time. These are snippet of codes that changed the way people thought about computer security, both the people designing the viruses and people trying to protect against them.

Melissa Virus

worst computer virus

Say it’s May 1999. You’re an unsuspecting computer user who’s never gotten a virus, let alone be trained to look for the signs that email may be malicious.

You get an email from someone with a subject you know, with a subject line that says it’s important message. The message inside just says “here’s document you asked for … don’t show anyone else” with wink emoji. The attachment is a Word document labelled “LIST”. So you click on it because you are curious and list of adult sites pop up.

At this point you realize the email was probably some kind of virus and it comes out be worst computer virus of all time. But it’s too late, the first 50 people in your address book have already gotten a copy of exact same email with subject line saying the message is from you. That was the Melissa Virus.

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worst computer virus

  • It spread through Microsoft Outlook email program, even though the attachment seemed like a innocent Word document, it was able to infect computer because of something called “Macro”.


  • In just few days, Melissa spread to hundred of thousands of computer. It didn’t do any damage to computer themselves but it did make email services slow way down and cost companies about $80 million overall.


  • The programmer behind the virus David L. Smith, was caught about a week after Melissa was first released. He spent 20 months in prison and paid $5000 fine.


ILOVEYOU Virus spread about a year after Melissa Virus in May 2000, was also successful because if social engineering. It reached about 45 million computers in just two days and caused about $10 billion dollar in damage and become the most destructive virus.

The infected email had the subject line “ILOVEYOU” and came with a attachment title “love-letter-for-you.txt”. When you clicked on the attachment the virus would go through the system files, looking for media, document and image files. Then it would overwrite itself with the ILOVEYOU folder, so if you didn’t have your file backed up, you’d lose all data. Meanwhile, the virus would be sent to every contact in your address book.

worst computer virus

  • ILOVEYOU kind of virus is called worm, which means that it was standalone program that didn’t use a host program to run and it turned out to be one of the worst computer virus in the world.


  • “love-letter-for-you.txt” was actually a file with  extension of visual basic script, which uses a file extension of “vbs”. The user couldn’t see the vbs at the end of filename, though, because of Windows OS they were using hiding file extension by default.


  • The virus was attributed to two programmers in the Philippines. But even though they were both arrested, they were released because at the time, there weren’t any laws against what they have done.

SQL Slammer

On January 25, just before 6 AM, the internet broke.

  • South Korea lost both internet and cellphone service
  • 300,000 people in Portugal couldn’t connect to the internet
  • Airlines couldn’t process tickets and had to cancel airlines
  • Bank ATMs went down
  • 911 in Seattle had to start using papers to log calls
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Even a lot of devices were still connected to the internet, the connections  had become suddenly very slow, even by 2003 standards. So  what happened?

As you can probably guess by now, all of these chaos was caused by Virus, yeah-the worst computer virus. But it wasn’t the kind of virus that spread through email, or infects the sort of computer most people have at home.

worst computer virus

  • Slammer was a worm that targeted SQL servers, which store databases using a piece of Microsoft software called Microsoft SQL Server. It worked by taking advantage of a bug in the software: it sent the server a specially-formatted piece of code, one that looked like it was just an ordinary request for information, but actually reprogrammed the server to send out more copies of the same worm.


  • The worm spread faster than any other virus ever had, infecting 75,000 servers in just 10 minutes. Those servers were all sending requests to thousands of other servers, which couldn’t handle all the traffic.


  • In all, millions of servers were affected, and the internet went kaput for a while. Slammer is thought to have caused about $1.2 billion in damage before it was stopped, and the programmer behind it was never caught.

2007 Storm Worm (Bot-net)

worst computer viruses

The 2007 Storm Worm was another worm that spread through email. But its purpose wasn’t to destroy your computer or information, it wanted to take over your computer instead. The original subject line read “230 dead
as storm batters europe,” which is where the virus gets its name.

But instead of an attachment, the email contained a link to a website, which promptly downloaded the virus onto the user’s machine. And then … nothing happened. Or at least, nothing the user could see.

worst computer virus

  • Storm Worm was designed to be as invisible as possible, so that you wouldn’t detect and destroy it. This way, it was able to use your computer to do all kinds of stuff in the background. The virus would connect your machine to what’s known as a bot-net, a collection of computers that form a network.


  • The programmers didn’t seem to be using it for anything nefarious, though, they just sold the network to other criminals and scammers.


  • After a while, companies did figure out how to stop the virus from spreading. They removed it from infected machines, and by late 2008, the Storm Worm bot-net was mostly gone. But, like with Slammer, the people behind it were never caught.


Mebroot is also a virus that slowly started to spread in 2007. And its main goal was also to hook you up to a bot-net, called Torpig. Both are especially sophisticated and yeah most destructive virus.

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Mebroot usually gets into your computer via a drive-by download, where you visit a malicious web page and the program downloads in the background without you even knowing it. From there, it overwrites what’s known as
the Master Boot Record, the part of your computer’s hard drive that stores the instructions that tell your computer how to start up.

Being able to control the Master Boot Record gives mebroot a lot of power, because it can tell your computer what to do right from the start. And what it tells your computer, is to connect to the Torpig bot-net … which then steals all of your information and turned out to be worst computer virus for all the user at that time.

worst computer virus

  • Torpig uses a spying technique known as Man-in-the-Browser, which is as creepy as it sounds. It lurks in your browser, logging everything you do and any private information you happen to enter.


  • It’ll also try to actively steal information, using fake websites that look and behave exactly like the originals, but send the data to the Torpig servers instead.


  • By late 2008, Torpig had stolen info connected to 500,000 bank accounts, and again, the people who created it haven’t been caught.

By now, you might be wondering whether a worm will make the internet go down tomorrow, or whether your computer is secretly part of a bot-net. And I don’t really blame you.

There are things you can do to avoid getting viruses:

  • Install an antivirus program
  • Don’t click on suspicious links or emails from Nigerian princes
  • Keep your operating system and computer programs updated with the latest security patches.

Computers are amazing, but they just do what they’re told, and when viruses tell them to do bad things, it can create a lot of damage.

Keep your systems safe.
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