The dirty digital dozen – 12 worst computer viruses in history

Ali Qamar Last updated: November 20, 2022 Read time: 16 minutes Disclosure

These 12 worst computer viruses have generated billions of dollars via stealth malicious activities.

Sneak peek at the worst computer virus attacks in history

With the advent of the first online virus in 1986, millions of computer viruses and worms infect computers daily, posing a severe threat to netizens’ online security. Such malware attacks are, so far, the most valuable tools of cybercriminals that can efficiently cause financial losses to the victim. This article lists the worst computer viruses in history that are still famous for their devastating damages.

Did you know the world’s first virus actually emerged more than three decades ago? Yes, apparently, the mother of all viruses, “Brain,” first surfaced online in 1986. Since then, many harmless or harmful malware have emerged and disappeared as cybersecurity people learned to cope with them. Nonetheless, a few of these are known for the worst computer virus attacks in the history of computer security.

This article tells you about the top 12 worst computer viruses to hit the digital arena. Furthermore, these viruses are all ranked according to the extent of financial damages they inflicted on the world. Hence, while they might not look so sophisticated, they undoubtedly proved to be the most successful viruses for cybercriminals.

The top 12 worst computer virus campaigns in digital history

Below we give you the costs, reach, key facts, and other details surrounding each virus. Nonetheless, this is by no means an extensive list of all digital viruses. Instead, they’re just the worst known malicious programs known to exist so far.

Every day, we have about 127 million pieces of malware attacking the digital denizens. So the list is infinite for any practical purposes. Our top twelve are the very worst but are not representative at all.

Not all the viruses listed below may fall into the category of “viruses” (technically). Instead, we have used the words “virus” and “worm” interchangeably here. This list merely intends to let you know the most devastating malware that have incurred huge financial damages until now.

1. Mydoom (38 billion)

The Mydoom outbreak is the worst virus attack ever to happen. Its estimated damage went as high as 38 billion USD (which would be 52.2 USD in current terms after adjusting for inflation). It also went by the name of “Novarg.” It was a worm that found its way around the internet mass emails. As this worm was active, it was responsible for about a quarter of the world’s email traffic.

As Novarg arrived into a system, it would scan it for fresh addresses. Then it sent copies of itself to those addresses. It also linked the infected computer into a botnet whose purpose was to carry out DDoS (Distributed Denial of Service) attacks. These attacks managed to shut down a website, or a server, by overwhelming it with junk traffic.

The funny thing about Mydoom is that it’s still around. But, unfortunately, it’s behind about 1% of the world’s phishing emails. If 1% strikes you as a meager fraction of those activities, think about this: the phishing traffic is currently about 3.4 billion emails daily. So that one percent represents thousands of millions of emails. So even 16 years after it was at the center of the world, Mydoom still has a life of its own, infecting those devices with the worse protection possible and still producing 1.2 billion copies of itself every year.

The Mydoom author was a wanted man. A quarter-million USD reward was available for his head, but nobody ever found him.


2. Sobig (30 billion)

Sobig appeared in 2003 as another worm, just like Mydoom. However, its success as the most dangerous cyber virus is second only to Mydoom’s as it managed to create about 30 billion USD in worldwide damage. It reached Europe, the US, and Asia. The authors released several Sobig versions quickly known from Sobig.A to Sobig.F. The last one was the worst.

This malware showed itself as a legitimate piece of software attached to emails.

It disrupted the activities of many businesses worldwide, with the Air Canada ticketing being the most famous problem during its time.


3. Klez (19.9 billion)

Klez appeared even earlier than the two previous worms in 2001. It’s remarkable that, as the world was not as interconnected back then, it still found its way into 7.2% of all PCs existing then on the planet. Klez would send fake emails, spoof known senders, and kill other viruses within a system.

Klez came in many flavors, as other viruses and worms often do. Also, it stayed alive and active for several years, hiding in many of the world’s active networks. During all this time, it kept evolving to release more dangerous iterations.