Top 10 Worst Computer Viruses of All Time

4 min read

How much damage can a computer virus cause? Well, lots of damage and billions of dollars. As people depend on computers nowadays to run almost everything, a widespread attack that affects those computers can be devastating not only to personal and business data, but also infrastructure.

Below are the 10 worst computer viruses that were ever made.

10. MyDoom

This computer worm is definitely up to its name. With the ability to email itself from infected computers, MyDoom was one of the fastest-spreading computer worms ever. This denial of service (DOS) worm attempts to crash websites by directing a huge amount of traffic to their servers.

At the height of the outbreak in 2004, MyDoom affected around 25% of all emails and caused damages to companies that are estimated to be around $38 billion. Major companies that were affected by MyDoom’s denial of service attacks included Google and Microsoft.


Despite the cute name of this computer virus, it’s definitely the furthest thing from what it claims to be. This is hands down one of the most destructive computer viruses that were ever made, and one of the most viruses to get media attention as well. When it was unleashed back in 2015, it was a disaster by all means.

Thanks to the tempting subject line “I love you” that this virus used when it emailed itself to unsuspecting victims, the infection rate was extremely high. In fact, the virus spread in a crazy way that it held a Guinness World Record as the fastest spreading virus ever.

Once this virus infects a computer, it overwrites itself on every single file that is on it.

8. CryptoLocker

Being a ransomware, CryptoLocker operates in a way that is different from traditional viruses. Once CryptoLocker affects a system, it simply takes the files hostage by encrypting them.

With all the files encrypted, users have one of two options: either they pay a ransom to decrypt their files or lose them forever. Once the victim pays, the files are decrypted and everything is back to normal. Unlike traditional viruses, ransomware are much more sinister. As it affected about half a million people back in 2014 –before the hackers were all arrested, CryptoLocker is definitely one of the most destructive malware of all time.

7. Storm Worm

This worm relied on people’s anxiety over bad news in order to spread. People would receive an email with the subject line “230 dead as storm batters Europe” –which is how this computer worm got its name, one they open the email to see what’s going on, their computers would get infected.

Infected computers were simply “enslaved” by the worm’s creator/creators and are used for things like sending spam email or as is what’s known as “zombie computers”. As this worm was detected in more than 200 million emails, it is definitely one of the worst spreading computer malware ever.

6. Anna Kournikova

No, this is not a coincidence. This computer virus was actually named after the famous Russian tennis player Anna Kournikova. The reason is quite simple, the person who actually wrote this virus used the popularity of this tennis player to spread this virus by emailing a picture of her.

Despite the fact that this virus isn’t as destructive as some of the other viruses on our list, it deserved a spot because of the unique way it used to spread.

5. Sasser

After being written by a 17-year old newbie coder, Sasser really got out of hand really quick, causing around $31 billion in damages. This virus was so devastating that it made 130 branches of a Finnish bank close down, caused many international flights to be canceled in additions to tons of additional damage.

As Sven Jaschan –the boy who wrote the virus- was a minor at the time, he spent the jail time in probation and later became an ethical hacker who works with many companies on security issues.

4. The Blaster Worm

This worm was targeted at Microsoft users. Using security issues in Windows XP and Windows 2000, Blaster was able to spread to millions of computers all around the world. In addition to infecting numerous personal computers, this worm launched a DOS on Microsoft’s website that caused a severe amount of damage.

Unfortunately, the person who wrote this malicious virus was never identified, making this one of the most mysterious cybercrimes of 2003.

3. The Melissa Virus

This fast-spreading email virus has caused around $1.1 billion of damages worldwide. After it infects a computer, the Melissa Virus disables are of the security measures on that computer and instantly emails itself to the first 50 names on the infected person’s contact list.

With so much damage caused and such a widespread level of infection, the Melissa Virus earned its spot on our list.

2. Stuxnet

What makes this virus really stand out from the other ones on the list is the fact that it was made by a government instead of some rogue hacker.

To hinder Iran’s nuclear program, engineers working for the United States Government wrote this virus to target the computers of Iranian nuclear facilities. Once it was deployed using a flash drive, this virus caused so much damage to the nuclear facilities that it set the Iranian nuclear program years back and cost the Iranian government lots of money.

Being a virus that was known to be developed by a government as a mean of cyber warfare makes Stuxnet pretty destructive and scary.

1. Slammer

Slammer is easily one of the worst computer viruses of all times for two reasons: the sheer amount of panic it caused and the insane way it spread.

Within 15 minutes of being deployed, Slammer was able to infect a third of the internet’s servers, which is by all means monumental. As this virus targeted many vital things like ATM machines, international flights, and emergency services, it caused a huge amount of panic for the general public, making it one of the worst computer virus outbreaks of all time.

With so many computer viruses and malware out there, backing up your important files is never a bad idea!