We rely on computers for an ever-increasing proportion of our day-to-day lives. As such, it can sometimes be hard to imagine how something so common and well-understood could ever lead to errors costing hundreds of millions or even billions of dollars.

Nevertheless, severe security flaws affect almost every single device on the planet (yes, likely including the one you’re reading this on right now), and rushed designs can claim hundreds of lives. Let’s take a look at ten times computers failed—or were made to fail—in expensive, sometimes even deadly, ways.

10 Mars Climate Orbiter

The Mars Climate Orbiter was a small space probe launched on December 11, 1998, by NASA to enter Martian orbit and both study the atmosphere of the Red Planet and provide valuable insight into its climate and any surface changes that might occur. The launch went as planned, and the probe traveled toward Mars with seemingly no issues, but unknown to the mission control team on Earth, the spacecraft was being put on a trajectory that would lead to the failure of the mission.

The orbiter was being navigated by various teams of people—some who used metric units, and others who used imperial units. Due to this simple conversion error—and the misconfiguration of the computer systems on the part of Lockheed—a course correction sent the Mars Climate Orbiter far too close to the planet, and it was likely violently burned up and destroyed in the atmosphere.^[1]

9 Ariane 5

Ariane 5 is a class of heavy-lift space rocket utilized in Europe. Jointly created by 20 European nations—including Belgium, France, Germany, and the United Kingdom—it has been continuously refined and altered to be more efficient, reliable, and powerful and is still in use today.

Following its initial development, the first fully completed Ariane 5 rocket lined up on the launchpad and prepared for its maiden flight on June 4, 1996.^[2] The rocket fired up the engines on both its core stage and its gigantic boosters and took to the skies, accelerating upward and beginning to turn at a much greater rate than its predecessor, the Ariane 4, as expected. Unfortunately, this was exactly why the rocket failed.

The internal computers and software responsible for monitoring speed and orientation aboard the Ariane 5 were reused from the Ariane 4, but the greater speed of the new rocket caused the computers to experience a “hardware exception” while converting a 64-bit floating point number to a 16-bit integer. Essentially, the more powerful rocket exceeded the limits of the older systems in just 37 seconds, causing the stored numbers to flip from 32,768 to – 32,768, confusing the rocket and initiating a sudden turn downward that resulted in a catastrophic breakup and aerial explosion, destroying both the rocket and its payload.

8 Knight Capital Group

Knight Capital was a American-based financial services firm buying and sharing stocks of huge value in large quantities on the global stock market. It was the dominant trader in the United States, with a share of approximately 17 percent on NASDAQ.

This all came crashing down at practically a moment’s notice on August 1, 2012.^[3] That morning, when the stock market opened, the automated computer systems based at Knight Capital began rapidly buying and selling millions and millions of shares distributed among hundreds of stocks for a total of 45 minutes, before the systems were isolated and stopped. Knight Capital was forced to sell these shares back at low prices, which resulted in a total net loss of over $440 million—or roughly $10 million per minute.

New trading software had been installed improperly on one of the computers by a technician, which caused the fault and destabilized the entire stock market for a short period. Following this debacle, Knight Capital had to be acquired by another financial firm, Getco, as the company simply lacked the money to continue and had to be “rescued” by other firms.

7 Stuxnet

Stuxnet is the name given to a piece of malware discovered in 2010 and thought to have been in joint development by the Americans and the Israelis as a cyberweapon since 2005. Targeting real-world mechanical systems, Stuxnet is generally regarded as the first known piece of malware intended to cause real-world, tangible damage.

Stuxnet appears to have mostly been employed against Iran’s nuclear program—infiltrating the nuclear facility at Natanz and infecting its computer systems, manipulating machinery in a destructive manner. It appears to have been snuck in via a simple, easily detectable USB drive, of all things. Between November 2009 and late January 2010, it is estimated that this malware caused 1,000 nuclear centrifuges—ten percent of the facility’s total number—to violently tear themselves apart by forcing changes in rotor speed.^[4] Stuxnet forced the centrifuges to first increase in rotation speed and then decrease in a highly effective attempt to cause instability. It is estimated that this destruction resulted in a 30-percent decrease in nuclear enrichment efficiency for Iran—a huge impact that undoubtedly hindered Iranian nuclear efforts.

6 WannaCry

In May 2017, a worldwide cyberattack was launched that infected Windows-based computers with ransomware. Ransomware is a form of malicious software that encrypts user data, making it unusable, and demands a payment to decrypt it and give it back to the user.^[5] WannaCry most significantly affected older Windows systems like Windows XP and spread to over 200,000 computers in 150 countries.

The ransom demanded between $300 and $600 per computer. Data was returned safely to those who paid the ransom. The United Kingdom’s National Health Service was especially badly affected, and tens of thousands of computers controlling MRI scanners, theater equipment, and more were attacked, causing some nonemergency cases to be turned away while the attack was contained. Worldwide, the cost is estimated at up to an enormous $4 billion, and the West has placed the blame squarely on North Korea’s shoulders.

5 Dhahran Patriot Missile Interception

The Patriot missile system is a United States-developed surface-to-air missile system capable of shooting down both aircraft and ballistic missiles, should they be detected and confirmed as enemy targets. It is widely employed today by both the United States and several of its allies, including Germany. It was also widely used in the Gulf War of 1991 to protect American soldiers and aircraft, which is where it failed due to a known software error.^[6]

A Patriot missile system installed in Dhahran, Saudi Arabia, had been operational for 100 hours, causing its internal clock to drift by 0.34 seconds. The Israelis had detected this issue two weeks earlier and advised the US to periodically reboot the system’s computers. This was not conducted. On February 25, 1991, a “Scud” ballistic missile launched by Iraq hit the US Army barracks in Dhahran, killing 28 American soldiers. The Patriot missile system had activated and detected the missile, predicting where to look for it next—due to the drifting internal clock, the system looked in the wrong place and found no missile, so it shut down and did not attempt an intercept, which could have saved many lives.

4 Meltdown

Meltdown is a vulnerability present in all Intel CPUs released between 1995 and October 2018, as well as some ARM processors. Given that the vast majority of all computers run Intel CPUs, security analysts describe the vulnerability as “catastrophic” and initially didn’t believe the reports of the vulnerability to be true, due to how severe they were.

Meltdown exploits the way modern CPUs function and allows processes running on a computer to see all information currently being used by the CPU by avoiding security measures designed to stop this. The implications of this are terrible—someone using Meltdown to attack a computer could see passwords, sensitive financial information, images, and practically anything they wanted without users’ knowledge, all while avoiding antivirus software.^[7] Intel has released emergency security patches to fix this exploit, as has Microsoft, but this has reportedly come at a cost of performance—from five percent to a whopping 30 percent. Given how widespread this exploit is, it is most definitely destructive.

3 Spectre

Spectre is similar in nature to Meltdown. It was also uncovered in 2018, but it’s even more widespread. While Meltdown is only effective against Intel CPUs for the most part, Spectre affects practically every single computer system as of 2019. It has been reported that some variants of Spectre cannot be mitigated to any reasonable degree by software changes at all and will require hardware changes which are currently being implemented.

Spectre works by tricking a program into accessing innocent-seeming memory but actually allowing an attacker to read this data and potentially retrieve sensitive information without user approval.^[8] As of this writing, only a very small amount of CPUs are immune to this exploit—most notably the recently released AMD Zen 2 processors and Intel Ice Lake processors. Software patches, like with Meltdown, are applicable but again introduce performance drops comparable to Meltdown, in addition to causing sudden, unexpected reboots as patches are applied. It is unlikely that Spectre will disappear completely for a very long time, until hardware mitigations are employed within every single computer system—and it is likely it is affecting you right now.

2 ILOVEYOU

Starting on May, 5, 2000, tens of millions of people around the world received an e-mail with the subject “ILOVEYOU.” The e-mail generally contained a small sentence like “Please read the attached LOVELETTER from me” and would have a file attached. The file was called “LOVE-LETTER-FOR-YOU.TXT.vbs,” and millions of people opened it out of curiosity—perhaps searching for love—causing the script contained within it to activate.^[9]

The hidden script would destructively overwrite random files on the computer and automatically send a copy of itself to every single address in Microsoft Outlook, causing it to spread extremely quickly. ILOVEYOU began in the Philippines and spread to Hong Kong, Europe, and finally the US. It is estimated that the malware caused approximately $8 billion in damages worldwide and cost around $15 billion to remove from computer systems. Ten percent of all Internet-connected computers in the world were affected, and 50 million infections were reported in just a span of ten days.

1 Boeing 737 MAX

The Boeing 737 MAX is a variant of the aging Boeing 737 line of narrow-body, twin-engine passenger airliners originally developed in the late 1960s. Since then, the 737 has been routinely updated and upgraded to fit in the modern world of aviation. However, it could be argued that the 737-MAX took this a step too far.

Rushed into development and production, the 737-MAX needed greater efficiency to keep its fuel costs as low as possible. To do this, it needed larger engines that could not be traditionally mounted on its wings. As a workaround, the larger engines were mounted further forward than normal, introducing a number of differences in the way it flies. To avoid the increased cost of pilot retraining for these new characteristics, Boeing instead implemented a system known as MCAS to mitigate these differences by automatically pushing the nose of the aircraft down when excessive angle of attack is detected. It was this software acting erroneously that led to the crash of two 737 MAX flights months apart: Lion Air flight 610 in October 2018 and Ethiopian Airlines flight 302 March 2019, claiming a combined total of 346 lives as the aircraft were forced into the ground by the MCAS system. Since these two crashes, the 737-MAX has been grounded worldwide and is not allowed to fly passengers due to safety concerns.^[10]

A guy from London, writing lists on anything he finds interesting—generally something scientific or technology-based.

How much memory do you have on your phone? An iPhone can have anywhere from a “bare bones” 64 GB to as much as a terabyte. Do you have an external hard drive for your gaming console? If so, it’s probably got at least a terabyte or two, right? And to think, if you bought a computer in 1995 it probably had around 12 MB of RAM and a hard drive of between 500 MB and a whole gigabyte. Memory has come a long way, and it offers a lot.

Dropbox currently offers you a terabyte of storage and translates that into practical terms. One terabyte is good for about 250 full movies. Or as much as 6.5 million pages of text. So with that in mind, let’s look at some memory figures. 

10. The Human Mind May Be Able to Store Petabytes of Data

Computer memory is most easily likened to our own memories, that’s why we use the same word. Your brain can hold information and so can a computer hard drive. It’s only natural to want to compare the two.

While a computer hard drive is pretty compact, it’s not like your brain is a vast expanse of material, either. But it has to be able to hold everything you can ever know. Everything you’ve experienced is in there, all the people you’ve met, things you’ve learned, recipes you’ve mastered, stupid movie quotes, random song lyrics, it’s all in there. So how much memory does a brain hold?

No one can say with accuracy exactly how much data your brain holds because, of course, your brain doesn’t work exactly like a computer. But it’s close enough that we can have some fun speculating, especially if you’re a computational neuroscientist and this is how you literally consider brain function.

Guesses for how much data a human brain can store range from a paltry one terabyte to a staggering 2.5 petabytes. We haven’t touched on petabytes yet and they are what come after terabytes. If a terabyte is 250 movies, and a petabyte is 1,000 terabytes, and a petabyte can hold 250,000 movies. Of course, you need to multiply that by 2.5 so it’s 625,000 full movies worth of storage. Or 16,250,000,000 pages of text. Decide for yourself if your brain can manage that. 

A few years after those initial estimates, researchers tried to narrow the range down and suggested a human brain could handle about one petabyte of information. To give that some non-movie context, that was about the size of all the information available on the internet in 2016 when the data was presented. 

9. You’d Need Unbelievable Space to Store a Yottabyte

A petabyte sounds big as hell if it’s all the internet or the equivalent of a lifetime of knowledge all crammed in the meatball inside your skull but it’s not the end of the line by any means. Numbers don’t end and the metric system dares not stop at peta, oh no. Have you ever heard of a yottabyte?

Yottabytes are well beyond petabytes. After petabyte comes exabyte, and then zettabyte, and then yottabytes. It’s the largest size that has been acknowledged so far by the International System of Units and represents one quadrillion gigabytes. 

Data has to exist somewhere and if there was a yottabyte worth of data in the world, which there isn’t, you’d have to put it on hard drives. Those hard drives, to accommodate that information, would cover a space of both Delaware and Rhode Island. You’d need a full million data centers to handle it all. 

8. 278,000 Petabytes of Traffic Flowed Through the Internet Per Month in 2021

Any time you’re online streaming content, reading social media posts, or doing whatever it is you do, have you ever wondered how many other people are doing the same thing? Or, more specifically, have you ever wondered how much information is flowing through those internet tubes all the time? The short answer is that it’s a lot.

Global internet traffic, which is all the internet activity in the world, in a given month, was estimated to be about 278,108 petabytes per month in 2021. In 2016 it was only 96,054. Elsewhere, it was predicted in 2022 that global traffic would surpass a more modest 150.7 exabytes per month in 2023, or 150,700 petabytes. 

7. It Would Take 500,000 Terabytes of Data to Map a Mouse’s Brain

We touched on how much info your brain might be able to store in it, but what if we wanted to map your brain? That’s a little more complex a question to answer than you might think. Mapping your brain means understanding all the neurons, all the synapses, all those hundreds of billions of connections that are needed to make it work the way it works. To map all of that would take a hell of a lot of time and data. 

Neuroscientists would love to map a human brain but it’s a tall order. It’s been estimated that, aside from the complexity of just pulling such a thing off, storing the information mapped would require about 1.3 billion terabytes of storage space. 

To at least broach the idea of mapping a human brain, researchers have looked at a smaller scale. Mouse brains are not as complex as humans though make no mistake they are still incredibly complicated. But mapping a mouse brain would take a lot less, at least.

Researchers are starting their task with a section of mouse brain, a tiny 10-square-millimeter segment. They expect mapping that small bit will take 10,000 terabytes of data. They’d need 50 times more, or 500,000 terabytes, for the full mouse brain. 

If the plan works as expected, all the data will show exactly how the brain works, and how all of those neurons function together to create a living, working brain.

6. In 1980, a 1 GB Hard Drive Weighed Over 500 Pounds

In your lifetime you have probably noticed how technology gets smaller as it gets more efficient. A desktop computer in the 80s barely had a fraction of the computer power that the phone you keep in your pocket holds. Memory condenses as technology improves and we can get a lot in a small space, something that keeps getting better and better with each passing year. Many people alive today have no idea what it was like forty years ago.

In 1980, IBM created a one GB hard drive. Today, a storage drive that only holds one gigabyte of data is all but useless to most people. You can store a good amount of text there, or some sound files, but you can’t fit a movie in a space that small and they haven’t made smartphones with so little memory in years. Amazon will sell you 50 one GB flash drives for just over $75, though. 

That one GB drive, when it debuted, cost $40,000. It weighed 550 pounds and was the size of a typical refrigerator. One of those 50 you can buy on Amazon will fit on your keychain. And, for the cost of the one from the 80s, you can buy over 26,600 of them. 

5. Data on Star Trek Has Less Storage Capacity Than Modern Supercomputers

When it comes to computers vs brains, artificial intelligence has to fit into the mix somewhere. And not the fake AI we have now which is just glorified text modeling, real AI. A computer that is alive and can think. So fiction, basically. Like Commander Data from Star Trek.

On the show, Data is essentially a computer in the form of a man that is capable of independent thought and understanding. He is self aware and, early in the show’s run, an episode establishes that he is alive, sentient, and not property. 

While establishing Data’s bona fides, his specs are also listed. The show was actually careful to not address a lot of specific technology about Data, especially later on, because the writers knew that what they thought was futuristic would quickly become outdated. But they still took the time to let us know Data’s storage capacity is 800 quadrillion bits. That sounds mildly impressive, but that breaks down to around 100,000 terabytes or 100 petabytes. 

100 petabytes is still remarkable, and it’s better than whatever device you’re looking at this on, but it’s not super futuristic anymore like it was back when that episode aired in 1989. The supercomputer called Aurora, which exists right here in the present, has a capacity of 220 petabytes. It’s already surpassed Data, it just hasn’t achieved sentience yet. That we know of. 

4. The Fastest Internet Ever Recorded Was More Than 7 Million Times Faster Than Average

Memory is important for any computer but so is speed. Who cares if you can store 1,000 movies if you have dial-up internet? Hey, remember dial-up? Speed is key to transmitting large amounts of data. In the US, the average internet speed is 219 Mbps download and 24 Mbps upload. 25 is considered fast, at least by the FCC, and basic is between three and 8. 

You may think 25 is not fast at all and you’re right, it’s not. It’s not even close. The fastest internet ever recorded was 319. And that wasn’t Mbps or even a basically unheard-of Gbps which you can only get with some good quality fiber service. That was Tbps—319 terabits per second. 

Japanese researchers broke the speed record in 2021 with a cutting-edge four-core optical cable. It’s so fast that, if you had it at home, you could download 80,000 movies in one second.

3. Frontier is the Most Powerful Computer Ever Built

We’ve covered a lot about memory, storage capacity, and even mentioned one supercomputer. But what is the best of all the supercomputers and what can it do? That would be Frontier, the current (but possibly replaced by the time you stumble on this list) most powerful supercomputer in history. It will always have a place in history as being the first exascale computer ever built. That means it can perform over one quintillion operations per second.

How does it do so much? It weighs nearly 270 tons, uses over 40,000 processors, and consumes more power than 15,000 houses.

2. Synthetic DNA Could Have 215 Petabytes of Storage Per Gram

As our ability to create more efficient storage increases, so too does the innovation in how it’s made. In recent years, the idea of using synthetic DNA as data storage has become more prevalent, in a theoretical sense. DNA holds all the information that makes up living things, after all, and it does so in microscopic packages. Lots of info, tiny space. It’s what computer dreams are made of.

If we could make synthetic DNA storage, it’s been estimated we could store as much as 215 petabytes of information in just a single gram of the stuff. 

As cool as it sounds, there are a couple of major drawbacks. One is that it takes a lot of time to read and write information to DNA storage. As in hours. No one wants to wait hours to save a file. But worse than that is cost. MIT once estimated that storing a single petabyte of data to DNA storage would cost about $1 trillion. 

1. Everything Ever Spoken Would Fill 5 Exabytes

We use outlandish examples of what data or memory represents to try to make it understandable. No one knows what a terabyte is when you just say terabyte. It’s a concept. But if you say it represents 250 movies, that makes it easier to relate to. Because you’re playing with ideas and concepts that represent big, monumental things, you can have some fun with it. You can get bigger.

How much memory would you need to record everything you have ever said in your life? It’s got to be a lot, right? But that’s still not big enough. What if we wanted to document everything anyone has ever said? Every word spoken in every language by every person who ever lived in the history of our species. How much would that be?  Best guess is 5 exabytes.

About 117 billion people have lived throughout history. At least one writer calculated that the average person, in their life, will speak 860.3 million words. Do the math on that and it’s a lot of words.

While computer viruses are still not as dangerous as actual, real-life viruses, they can still cause a significant amount of damage if they’re left out in the open and allowed to infect a large number of computers – much like their natural counterparts. In the past few years, viruses and other similar types of mass cyber attacks have managed to cause a lot of real harm to people and businesses around the world, often in the form of loss of crucial data and financial damages. 

10. Stuxnet

The Stuxnet worm was discovered on June 17, 2010 by an antivirus firm called VirusBlokAda. Widely considered one of the most sophisticated cyber weapons ever created, it was a malicious computer program that was designed to target industrial control systems, specifically those used in Iran’s nuclear program. The worm was able to infiltrate the country’s computer networks and spread rapidly due to its aggressive nature, soon spilling outside the borders of its intended target.

Stuxnet was a type of cyber attack known as a “worm,” which is able to self-replicate and spread from one computer to another without human intervention. In the case of Iran’s nuclear program, Stuxnet was specifically designed to target the centrifuges used to enrich uranium, causing them to malfunction. According to reports, the worm was successful in infecting thousands of computers, along with setting Iran’s nuclear program by several years, especially due to its sabotage of the systems at the Natanz nuclear facility. 

9. MyDoom

MyDoom, also known as Novarg, is a malicious computer program discovered in January 2004. It’s a worm-type virus that spreads through email attachments, file-sharing networks, and other channels. Once a computer is infected, MyDoom can use it to send out spam emails, launch denial-of-service attacks, and collect sensitive information, among a bunch of other harmful applications.

MyDoom usually arrives in emails with subject lines that appear legitimate, often tricking users into downloading and running the malicious code. It caused quite a bit of damage and disruption in its early days, infecting millions of systems and causing about $38 billion in damages. 

MyDoom was also responsible for a number of high-profile denial-of-service attacks, including the one against Microsoft, resulting in their websites being unavailable for several days. According to one estimate, the virus infected about 1 in 12 emails at its peak, making it one of the largest cyber attacks in history. 

8. Klez

The Klez virus was a mass-mailing worm first detected in December, 2001. Its first variant was capable of spreading through email attachments and Internet Explorer, primarily affecting computers running Microsoft Windows. Since then, multiple, advanced variants have been discovered, including ones that can easily spoof email addresses from authentic sources.

The Klez virus and its variants are particularly dangerous due to their ability to modify or delete files on an infected computer. It can also steal email addresses and passwords, making it a major threat to the data stored by personal and business computer users. Some Klez versions are even capable of disabling antivirus software and creating backdoors for hackers to gain access to the machine, leading to more serious crimes. The Klez virus caused global damage in the early 2000s, as it infected millions of computers and email servers worldwide. 

7. SoBig

The Sobig virus first started infecting computers in 2003. It was a kind of a computer worm that used email and shared network folders to spread rapidly to other computers. Sobig even had the ability to create its own server, allowing it to send out infected emails to thousands of users without a host email account. At the time, it was also called the fastest e-mail virus outbreak in history, far surpassing the previous record held by Klez.

Sobig specifically targets computers running on Microsoft Windows. Much like other successful viruses, it uses the tried-and-tested email network to spread around, specifically email attachments. At its peak, more than 1 million copies of Sobig were found in emails around the world, as reported by a digital security firm called MessageLabs Inc. Apart from causing real-life financial losses, the virus also had an immeasurable impact on people that lost valuable data or documents in the attack.

6. Zeus

Zeus was a type of Trojan virus first discovered during a cyber attack against the United States Department of Transportation. It’s a financial or banking virus, designed to steal sensitive information from infected computers like banking credentials, credit card numbers, and other personal details. While it could pass around in a number of ways, the Zeus Trojan primarily spread through email attachments, malicious downloads, or vulnerabilities in web browsers and other online software.

Zeus can remain hidden and undetected for long periods of time, as it gets lodged in a computer or security system and continuously captures sensitive data to send it back to the attackers. Later variants were even capable of keylogging, taking screenshots, and stealing login credentials from user activity. Zeus has been known to target financial institutions, government agencies, and corporations, making it a significant threat to everyday users and large organizations alike.

5. CryptoLocker

CryptoLocker is now a fairly well-known type of malware that encrypts a victim’s files and demands payment in exchange for the decryption key, or some other variation of it. It can spread in a variety of ways, typically email attachments, file-sharing sites, and downloads. CryptoLocker primarily targets Windows users and has been known to rapidly spread across networks if left unchecked. 

Once installed on a victim’s computer, the malware encrypts files using a strong encryption algorithm, making them inaccessible without a password or key only known to the hacker. They then demand payment in exchange, usually in the form of Bitcoin or other cryptocurrencies. Depending on the victim and attacker, the ransom could range from a few hundred to several thousand dollars.

CryptoLocker is what we know as ransomware – a specific type of malware that causes damages worth billions of dollars around the world every year. It can even shut down systems critical for public safety and well-being, like hospitals and government agencies, until a ransom is paid out, making it all the more dangerous in the larger scheme of things.

4. PlugX

PlugX is a type of Remote Access Trojan (RAT) used by cybercriminals for a specific type of cyber attack known as an Advanced Persistent threat (APT) attack. RATs are malicious software that give attackers remote access to a victim’s computer, allowing them to control it like they were physically there. PlugX is typically delivered through targeted phishing emails or software vulnerabilities. Once installed, it can give attackers complete control over an infected system, allowing them to steal data, execute commands, and install additional malware.

PlugX has been linked with the military, as it has been used in targeted attacks against government agencies, defense contractors, and other high-value targets. It’s particularly effective at evading detection by security software, as it can remain undetected on a compromised system for long periods of time. Once an attacker gains access, they can use PlugX to attack the machine itself, or infect it and use it as a jumping-off point to other, more important systems on a network.

3. NIMDA

The Nimda virus was first detected in September 2001. It’s a sophisticated piece of code that spreads through multiple attack routes, including email, websites, and network shares. The virus combines the best techniques used in worms, viruses, and Trojan horse kind of attacks, and was capable of infecting both servers and workstations running on Microsoft Windows.

The Nimda virus has so far caused hundreds of millions in damages, as it can easily spread through features we use every day, like email attachments. Unlike other viruses, Nimda didn’t seek to cause harm to the files or network security of systems. It went for the more delayed, chaotic effect by slowing down the entire network for extended periods of time, usually by sophisticated denial-of-service attacks. Nimda is also capable of exploiting known vulnerabilities in web servers, allowing it to infect a large number of computers in a short period of time.

2. Fizzer

The Fizzer worm was first detected in 2003 by the antivirus firm Kaspersky Labs. It’s a complex and sophisticated malware, with the ability to spread through multiple channels like email, instant messaging, and file-sharing networks. When it was first discovered, Fizzer was rapidly spreading through the Kazaa network, as it infected a large number of computers before it could be found. 

Once installed on a computer, the Fizzer virus can perform a wide range of malicious actions, like stealing passwords, credit card numbers, and personal data, along with disabling security software to open backdoors for more advanced actions. Some versions have even been known to send infected emails to the victim’s contacts, increasing the likelihood of further infection to other systems. Fizzer remains one of the most widespread viruses in the world, even if it’s no longer as effective as it used to be back when P2P file-sharing was still popular.  

1. Sircam

The Sircam worm was discovered in July 2001, and it quickly became one of the most widespread and damaging computer viruses of all time. It was designed to primarily spread through email and network shares, using a variety of tricks to lure users into opening infected email attachments. Once installed on a system, the worm would attempt to spread to other computers on the same network, combined with malicious actions like deleting files and sending itself to all the contacts in the user’s email address book.

Sircam caused billions in damages and infected millions of computers worldwide, largely due to its resilience and highly-infectious nature, as it was difficult to detect and remove in many cases. At its peak, Sircam accounted for a large percentage of virus infections online, making it one of the largest security threats ever. Thankfully, Sircam is no longer as active as it once used to be, though it remains a threat for certain legacy Microsoft operating systems still in use for specific purposes.