Most Destructive Computer Viruses in History

Most Destructive Computer Viruses in History

From Mydoom to Code Red—here are some of the deadliest computer viruses you need to know about!

In 2021, nearly 74% of businesses experienced malware activity that spread from one employee to another. More than 350,000 new kinds of malware are discovered each day and as of 2020, businesses spend around US$55 billion per year dealing with computer viruses. 

Just like a real-life virus, dealing with a computer virus can be a tremendous challenge. They cause problems that cost a lot of money to fix and also take away from the time that could have been spent being productive. Plus, not all viruses are made alike, meaning that the level of havoc and destruction a virus can cause inside your computer varies. With that said, here are some of the most deadly computer viruses in history.


Mydoom is a computer virus that spreads itself by sending spam emails to email addresses collected from an infected computer. It also creates a network of infected computers, which is called a botnet, to perform distributed denial of service (DDoS) attacks (attacks which flood targeted websites with fake traffic, making them unavailable to legitimate users). The virus has been around since 2004, and estimated damage reached US$38 billion that year. It continues to attack devices, and nearly 1% of all phishing emails ever sent are generated by Mydoom. 


Created by two Filipino programmers, this computer virus used social engineering to get people to share their personal information. The virus would reach you as an email attachment posing as a love confession. Once you click onto the attachment, the virus would send itself to your entire mailing list and overwrite files, making it impossible to boot your computer. Created in the year 2000, the ILoveYou virus infected 10% of the world’s computers in its heyday and costed US$10 billion in damages. 


Released in 2013, CryptoLocker is ransomware that was spread through email attachments and encrypts the files on the computer, rendering them inaccessible. While it was not hard to remove the ransomware from your computer, the files encrypted by it would stay inaccessible until you find a decryption key. To access the key, you would have to pay a certain amount in Bitcoin as a ransom (US$400 on average) within a stipulated period of time. If you didn’t meet the deadline, either the ransom would increase or the key would be deleted. The virus hit 5,000 companies and ended up costing them a cumulative US$655 million.


CodeRed was first discovered by two eEye Digital Security employees in 2001. The ransomware was named CodeRed because the duo was drinking Mountain Dew Code Red at the time. This ransomware targeted computers with Microsoft IIS web server installed, exploiting a preexisting issue inside the server. Infected computers would deliver a DDoS attack on the U.S. White House’s website, which invariably forced the White House to change its IP address. It caused damage worth US$2 billion and affected one to two million servers. 


Created by David L. Smith in 1999, the mass-mailing virus Melissa (named after a stripper he met in Florida) was circulated as a Microsoft Word document with passwords to pornographic websites. At the time, people were not as suspicious of email attachments as we are today, and people readily downloaded the document. Once they opened it, it would send itself to the top 50 people in their address books. This hampered email traffic and servers worldwide, such as those of Microsoft and the United States Marine Corp, causing US$80 million worth of damage. The creator of this virus was sentenced to 20 months (originally up to five years) in jail and was fined US$5,000. His sentence was reduced after he agreed to help the U.S. Federal Bureau of Investigation (FBI) identify some other computer viruses and the masterminds behind them.

How can you tell that your device has a virus?

There are some telltale signs that your device might have a virus in it. If your computer is suddenly performing tasks at a much slower speed than usual, has problems shutting down, restarting or crashes unexpectedly, chances are you might be dealing with a virus. Some other common signs of a virus are unexpected pop-ups, applications showing up without being downloaded, an overworked hard drive (loud sounds of the device fan whirring) and malfunctioning antivirus software.

You can protect your device from viruses by using virus protection software, keeping your device up-to-date and using virtual private networks (VPNs) when accessing public Wi-Fi. Make sure to not click on suspicious links, call-to-action buttons (like one that says “Click Me”),  or email attachments and avoid downloading pirated content. 

Header image courtesy of Freepik


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