Computers viruses, worms, ransomware, etc. are kinds of malicious software that no user should take lightly. On several occasions, we have touched upon security steps that each user should take in order to protect its identity and data. Sadly sometimes even when all precautions are taken some malware can still slip through and wreak havoc. Today we are looking at some of the worst or the best, depending on your view that has indeed wreaked plenty of havoc.
10 worst computer viruses in history
In the list of the 10 most famous computer viruses below, we show the costs, dates, reach, and other key facts. First a note about terms: we use the words “virus” and “worm” interchangeably because most readers search for them that way. But there’s a subtle difference that we explain after the list.
1. Mydoom – $38 billion
The worst computer virus outbreak in history, Mydoom caused estimated damage of $38 billion in 2004, but its inflation-adjusted cost is actually $52.2 billion. Also known as Novarg, this malware is technically a “worm,” spread by mass emailing. At one point, the Mydoom virus was responsible for 25% of all emails sent.
Mydoom scraped addresses from infected machines, then sent copies of itself to those addresses. It also roped those infected machines into a web of computers called a botnet that performed distributed denial of service (DDoS) attacks. These attacks were intended to shut down a target website or server.
Mydoom is still around today, generating 1% of all phishing emails. That’s no small feat considering the 3.4 billion phishing emails sent each day. By that figure, Mydoom has taken on a life of its own, infecting enough poorly-protected machines to send 1.2 billion copies of itself per year, 16 years after its creation.
Though a $250,000 reward was offered, the developer of this dangerous computer worm was never caught.
Wondering what makes the world’s most secure computers so safe? See the Tech@Work guide: Upgrade to the World's Most Secure and Manageable PC
2. Sobig – $30 billion
The 2003 Sobig computer virus is actually another worm. It is second only to the Mydoom virus in its scope. The $30 billion figure is a worldwide total, including Canada, the U.K., the U.S., mainland Europe, and Asia. Several versions of the worm were released in quick succession, named Sobig.A through Sobig.F, with Sobig.F being the most damaging.
This cybercriminal program masqueraded as legitimate computer software attached to emails. It disrupted ticketing at Air Canada and interfered with countless other businesses. Despite its widespread damage, the creator of the successful bug was never caught.
3. Klez – $19.8 billion
Klez is a close third on the list of the worst computer viruses ever created. With nearly $20 billion in estimated damages, it infected about 7.2% of all computers in 2001, or 7 million PCs. The Klez worm sent fake emails, spoofed recognized senders and, among other things, attempted to deactivate other viruses.
As with other viruses and worms, Klez was released in several variants. It infected files, copied itself, and spread throughout each victim’s network. It hung around for years, with each version more destructive than the last.
Windows has come a long way since most of the computer viruses on this list hit the web. Thankfully, built-in protection with Microsoft Defender is always on the watch.
4. ILOVEYOU – $15 billion
The year 2000’s ILOVEYOU virus worked by sending a bogus “love letter” that looked like a harmless text file. Like Mydoom, this attacker sent copies of itself to every email address in the infected machine’s contact list. Shortly after its May 4 release, it had spread to more than 10 million PCs.
The virus was created by a college student in the Philippines named Onel de Guzman. Lacking funds, he wrote the virus to steal passwords so he could log into online services he wanted to use for free. He reportedly had no idea how far his creation would spread. This virus is also known as Loveletter.
Need to up your remote work security game before there’s another entry on the list of most deadly computer viruses? See our guide: How to Work Remotely and Securely
5. WannaCry – $4 billion
The 2017 WannaCry computer virus is ransomware, a virus that takes over your computer (or cloud files) and holds them hostage. The WannaCry ransomware ripped through computers in 150 countries, causing massive productivity losses as businesses, hospitals, and government organizations that didn’t pay were forced to rebuild systems from scratch.
The malware raged like wildfire through 200,000 computers worldwide. It stopped when a 22-year-old security researcher in the U.K. found a way to turn it off. Computers with out-of-date operating systems were hit especially hard. That’s why security experts always recommend updating your systems frequently.
Ransomware strikes again
In September 2020, one of the potentially largest computer virus attacks in medical history hit Universal Health Services. The U.S. hospital chain, which has more than 400 locations, was reportedly struck by damaging ransomware. The attack forced the cancellation of surgeries and made healthcare workers switch to paper records.
6. Zeus – $3 billion
The Zeus computer virus is an online theft tool that hit the web in 2007. A whitepaper by Unisys three years later estimated that it was behind 44% of all banking malware attacks. By then, it had breached 88% of all Fortune 500 companies, 2,500 organizations total, and 76,000 computers in 196 countries.
The Zeus botnet was a group of programs that worked together to take over machines for a remote “bot master.” It originated in Eastern Europe and was used to transfer money to secret bank accounts. More than 100 members of the crime ring behind the virus, mostly in the U.S., were arrested in 2010. It’s not as prominent today, but some of the virus’ source code lives on in newer botnet viruses and worms.
Zeus caused documented damage of $100 million. But the real cost in terms of lost productivity, removal, and undocumented theft is undoubtedly much higher. A $3 billion estimate, adjusted for inflation, puts this virus at a cost of $3.7 billion in today’s dollars.
7. Code Red – $2.4 billion
First observed in 2001, the Code Red computer virus was yet another worm that penetrated 975,000 hosts. It displayed the words “Hacked by Chinese!” across infected web pages, and it ran entirely in each machine’s memory. In most cases it left no trace in hard drives or other storage.
Financial costs are pegged at $2.4 billion. The virus attacked websites of infected computers and delivered a distributed denial of service (DDoS) attack on the U.S. White House’s website, www.whitehouse.gov. In fact, the White House had to change its IP address to defend against Cod Red.
Can your printer get a virus? See our cool infographic: The State of Printer Security
8. Slammer – $1.2 billion
The SQL Slammer worm cost an estimated $750 million across 200,000 computer users in 2003. This computer virus randomly selected IP addresses, exploiting vulnerabilities and sending itself on to other machines. It used these victim machines to launch a DDoS attack on several internet hosts, significantly slowing internet traffic.
The Slammer worm hit banks in the U.S. and Canada especially hard, taking ATMs offline in many locations. Customers of Toronto’s Imperial Bank of Commerce found themselves unable to access funds. The attack reared its ugly head again in 2016, launching from IP addresses in Ukraine, China, and Mexico.
9. CryptoLocker – $665 million
Thankfully, ransomware attacks like the 2013 CryptoLocker virus have dipped since their 2017 peak. This malware attacked upwards of 250,000 machines by encrypting their files. It displayed a red ransom note informing users that “your important files encryption produced on this computer.” A payment window accompanied the note.
The virus’ creators used a worm called the Gameover Zeus botnet to make and send copies of the CryptoLocker virus. According to a report by security firm Sophos, the average ransomware attack costs a business $133,000. If we estimate that CryptoLocker hit 5,000 companies, that would put its total cost at $665 million.
Where will cybersecurity go next? See our guide: The Future of Cybersecurity
10. Sasser – $500 million
The Sasser worm was written by a 17-year-old German computer science student named Sven Jaschan. He was arrested at the age of 18 in 2004 after a $250,000 bounty was posted for the computer virus’ creator. A friend of Jaschan’s tipped authorities that the youth had penned not only the Sasser worm but also the damaging Netsky.AC attack.
Jaschan was given a suspended sentence after it was found he was a minor when he wrote the malware. The Sasser worm crashed millions of PCs, and though some reports put damages at $18 billion, the relatively low infection rate suggests a more likely cost of $500 million.
Other notable viruses
The top 10 worst computer viruses above are just the ugly tip of a gargantuan digital iceberg. With a million new malware programs popping up every 3 years, we may miss the forest for a few outstanding trees. Here are just a few more viruses that have wreaked havoc over the years:
Mimail: This worm tried to harvest data from infected machines to launch a string of DDoS attacks, but was relatively easy to remove.
Yaha: Yet another worm with several variants, thought to be the result of a cyber-war between Pakistan and India.
Swen: Written in C++, the Swen computer worm disguised itself to look like a 2003 OS update. Its financial cost has been pegged at $10.4 billion, but not reliably.
Storm Worm: This worm showed up in 2007 and attacked millions of computers with an email about approaching bad weather.
Tanatos/Bugbear: A 2002 keylogger virus that targeted financial institutions and spread to 150 countries.
Sircam: A computer worm from 2001 that used counterfeit emails with the subject line, “I send you this file in order to have your advice.”
Explorezip: This worm used fake emails to spread to every machine on thousands of local networks.
Melissa: The most dangerous computer virus in 1999, Melissa sent copies of itself that looked like NSFW pics. The U.S. FBI estimated cleanup and repair costs at $80 million.
Flashback: A Mac-only virus, Flashback infected over 600,000 Macs in 2012 and even infected Apple’s home base in Cupertino, Calif. In 2020, there’s now more malware on Macs than on PCs.
Conficker: This 2009 virus still infects many legacy systems and could do significant damage if it ever activates.
Stuxnet: This worm is reported to have destroyed Iranian nuclear centrifuges by sending damaging instructions.
So far we probably all know what are good new and exciting features that W11 is bringing to the table, let’s talk now about features that will be removed and are not there but we had them in W10
EVE Online is one of the earliest MMO games out there but since its release, it is still actively developed and is receiving updates. This science-fiction Sandbox will offer space lovers everything they need and more. Large scale PvP, mining, pirating, etc. It can be daunting and complex for beginners but take your time to get familiar with its systems and you will be rewarded greatly with an immersive and complex game worth the time. Open PvP in some zones might not be everyone’s cup of tea and seeing only your ship might be a turn-off for some players, but if you do not mind these things give it a go. It is free to play with an item shop.
FF14 had a tough start, so tough that it was scrapped and destroyed and has been remade again and that idea was great. The game now is better than ever and at this time it is experiencing large players from other games surging into it. This on the rails fantasy MMO will offer you a great story and great leveling experience. It has a free trial where you can play the whole original game for free but if you wish to continue playing you will have to buy the expansion and pay a monthly subscription but the content is well worth the money.
Let’s be honest, not a single list of MMO games cannot be without a once greatest and most successful MMO ever made, World of Warcraft. But instead of me praising the game why it was the greatest and why you should play it and how great it is I am going to take a little different approach. I am going to recommend you World of Warcraft classic, yup, you read it correctly, classic. Now World of Warcraft is a retail game with a subscription service but with that one subscription you will be able to access three games in the World of Warcraft universe: World of Warcraft retail (standard game), World of Warcraft Classic (vanilla WOW without expansions offering you experience as it once was when it was released) and World of Warcraft the Burning Crusade classic (same as WOW classic but with the first expansion the Burning Crusade). Among all solutions, I would really urge you to play either WOW classic or WOW TBC classic simply for reason that they are far superior games in comparison to typical retail ones, but if you like easier game go for retail, it is included in the sub anyway.
Guild Wars 1 was one of my favorite games and I sank a lot of times in it and once Guild Wars 2 came I must admit I was pleasantly surprised with it and I would recommend it highly. The base game is completely free to play with only expansion to be purchased and it is buy to play model without monthly fees. It has specific mechanics different from other games and interesting classes to try. The living world is a great feature of the game and it is still very strong with its player base.
This game is made for people who enjoy, love, and like Star Wars. Mechanically besides being able to have henchmen with you and space battles (which I do not really like how they are done) game itself does not offer anything special. Where it shines is in the story and overall Star Wars experience. If you look at this game as a single-player game with multiplayer dungeons you will have a great time, since the story is really good but sadly end game lacks in comparison.
I am going to admit something here, I was not fond of the idea to make the beloved Elder Scrolls series into MMO, but in time I gave it a go and I am really glad I did. This game is great and it is getting better and better as time progresses. It is buy to play without monthly fees and basic game free, same as FF14 but without fees. It has a decent community and offers a really good Elder Scrolls experience and now it is packing Morrowind expansions and other great areas. Highly recommended for any Elder Scrolls fan.
This one is troublesome to recommend, on one side you have free to play games deeply inside Tolkien Lord of the Rings lore, on the other side, you have outdated graphics and some stupid item shop decisions like buys specific classes. But if you look past stupid item shop decisions and can live with playing free class in the game you will be pleasantly surprised. The game itself is surprisingly good, the story is great as expected from the game infused with lore taken from one of the best books series ever written, and the feeling when visiting iconic landscape is epic. But if I need to be real as I should, I would recommend this one to people appreciate good story and lore and ones that are fans of Lord of the Rings itself.
Neverwinter is a premium and licensed D&D MMO game and it is well strange. The free-to-play model of the game will let you enjoy it until you hit the end game, then you will have to shell real money if you want to be competitive but the journey until then is great. I would recommend it to D&D lovers and people that love to try other people's maps, yup you read it correctly. Neverwinter has a map editor making it one of a kind MMO game where you can create your own dungeons and post them for other players to play, this user-generated content makes it a very specific beast in this list, and for that feature alone it has my recommendation.
Another one of the older titles, Tera will offer you nor depth nor anything new in terms of leveling, quests, or end game except… the COMBAT. This is maybe the greatest MMO Combat game ever created and it is quite fascinating that even after so many years no other game has managed to create a better combat system than one of Tera. If you enjoy action combat and like some specific aesthetics Tera is a game for you.
Albion is a sandbox game with open-world PvP and building mechanics where you can build your own forest, house, etc. You know, sandbox stuff, including a lot of crafting and well, other sandbox stuff. If you want great quests and some occasional play then skip Albion, this game is made for a more hardcore player base not being afraid to die and spend some time crafting and going through the economy. The best comparison might be with EVE but in fantasy settings.
Black Desert is also a sandbox game but different from Albion, here you can organize and hire a workforce and send them to different nodes on a map to harvest resources and build an economy while you are on some epic adventure. Housing is also included but you can buy already made houses instead of making your own in the world. Combat is a game that comes very close to Tera combat and it is very enjoyable. The end game is money sink and PvP based so be careful when choosing this one.
If you like occult and supernatural with new world order themes and conspiracy theories, Secret World Legends is the game for you. Somewhat little clunky its setting and story really set it apart in many many ways. It has semi-action combat and it is free to play with item shop but all the content can be experienced for free. Recommended for fans of deeper gameplay and horror lore.
When I said no MMO list can be without World of Warcraft, it also cannot be without Runescape, one of the oldest games it was revamped with newer mechanics and graphics, free to play all the way and you can also pick old school Runescape if you really want to go all the way on a nostalgia trip. I would recommend a newer one for newer players, the game offers a great story and unusual quests infused with puzzles and interesting storylines. If you like really good quest design without fetch and grind quests along with interesting story this is a game for you.
Last on my list would be AION, a very interesting game made also a long way back, but the fact that is completely free with the cosmetic shop will make it as one to recommend since you can experience the whole game for free. It has some limited flying mechanics in it and later game zone are open PvP zones, story is interesting and leveling process is enjoyable. Also game itself is not really easy and if not careful you can get yourself in danger quite quickly. Recommended for old-school feeling.
Many times we were talking and writing here on Errortools.com about security, privacy, hacking, identity theft, etc. We tried to raise important security questions and I hope I have managed to at least shed some light and change maybe some bad behaviors for some, helping them embrace better routines about their security on their PC.
In this light, I will today present you with one neat and awesome piece of software, a password manager worth your time and money (if you want premium features): BitWarden.
