Top 7 Most Dangerous Viruses in History

Computer viruses are not the most pleasant things to deal with. Discovering that you caught one can be pretty stressful and come with serious consequences especially if you run a business and haven’t hired a gdpr compliance company. Viruses can cause you to lose access to your social media accounts and have your bank account hacked. Fortunately, the history of computer viruses is much more interesting and fascinating than dealing with a virus yourself.

Are you keen on educating yourself on the topic? If that is the case, then you are in the right place! In this article, you will find a list of the most dangerous computer viruses, ranging from Sasser, CryptoLocker, and Slammer to WannaCry, ILOVEYOU, and Klez. Check it out!

Morris Worm

This worm is infamous for becoming the first computer worm to be released into the wild and has the potential to crash every unprotected computer it encounters. It was released back in 1988 by Cornell University graduate student Robert Tappan Morris, who was just 22 years old at the time. Even though he was convicted of violating the Computer Fraud and Abuse Act and sentenced to three years of probation, he was not charged with any violation of federal law. It is estimated that this worm infected over 6,000 UNIX systems and caused approximately $100,000 worth of damage.


This is a famous computer virus that is believed to have been written by a 15-year-old hacker from India. It was first spotted in 2001 and had a significant impact on several large websites, such as eBay, Yahoo!, and MSN. In addition, Nimda also infected thousands of Windows computers, which led to a massive DDoS attack against an online security site.

ILOVEYOU/Love Letter

The “ILOVEYOU” virus was first spotted in May 2000. It spread like wildfire around the world and, within just one day, it made its way into millions of inboxes all over the world. Interestingly enough, this computer virus contained the word “love” in its name which is something that might have contributed to its level of success in the beginning. ILOVEYOU is considered one of the most dangerous viruses in history due to the fact that it was able to erase certain data from the affected computers. Consequences were limited only to the files stored on the affected computers and did not cause financial damage or disruption of any kind.


One of the most complex computer worms at the time, Sasser was first spotted in 2004. This virus was able to spread quickly through networks and take advantage of known security vulnerabilities in order to infect thousands of personal computers and servers all over the world. Sasser also affected many businesses that rely on their IT infrastructure for everyday operations. The worst part is that after being finally eradicated in 2005, another version of it appeared called Sasser. B. This made it one of the few computer viruses in history that had more than one version of itself.


Another dangerous computer virus that went viral in 2003, Slammer infected more than 75,000 Microsoft SQL servers worldwide. It caused major disruptions and is believed to have cost businesses all around the globe millions of dollars in damages. The worst thing about this virus is that it can be transmitted via network packets, which means that there is no need for an infected machine to connect directly to a vulnerable machine for Slammer to spread itself. This can be done by simply sending out infected packets over the network in question. The worm only needs to be executed by one vulnerable machine connected to the network for it to be completely immune from detection. Once it starts spreading, it will reach vulnerable systems in less than two minutes, making it one of the fastest worms ever created during its time period.

Code Red Worm

A variation of the Code Red worm first appeared back in 2001 and managed to infect almost 250,000 computers around the world. This worm comes with a rootkit which makes it impossible for antivirus software companies to detect it during their regular scans. After being transported throughout the Internet by an infected machine, the worms were able to scan for vulnerabilities on Windows NT 4 (any system on NT 4 using port 1434) before launching a brute force attack against them. As a result, you can imagine what happened next, every server that did not have a firewall enabled was affected by this virus or its variants!

Melissa Virus

First spotted back in 1999, this virus was one of the first viruses that was able to spread via Microsoft Word documents and email attachments. One of its main goals was to send itself to all contacts found within Microsoft Outlook. Melissa was one of the first viruses ever created that exploited new techniques used by antivirus software companies in order to avoid detection during scans – which increased its popularity and success rate significantly. The name “Melissa” has nothing to do with Melissa Joan Hart or her TV show Melissa & Joey but rather refers to Melissa virus’ creator, Melissa O’Neil of New Zealand, who passed away due to leukemia when she was only 29 years old. She did not create this virus with malicious intent but rather as a joke which backfired pretty badly on her in the end!


Now it’s safe to say that most people have had an unpleasant experience with a virus at least once in their lifetime. Probably not as bad as the ones mentioned on this list though! In saying that though, viruses can cause a lot of damage. They can hack your social media pages, bank accounts, they can destroy your files, or even damage your pc or phone to a point where it is impossible to repair. So not only can they destroy what’s inside your computer, but you might have to buy a whole new one. Thankfully, these days, that is pretty rare because there is a lot of security available out there for these reasons. If you don’t already have something in place to protect you from viruses, we suggest you do so as soon as possible. So what did you think of this list? Have you heard of these viruses?

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