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.
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.
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.
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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.
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.
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
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.
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.
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.
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
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.
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
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.
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Some users installing or upgrading to Windows 10 experienced the theKMODE_EXCEPTION_NOT_HANDLED Blue Screen of Death (or commonly known as BSOD) error. This error can be due to different types of things, ranging from software to driver issues. When you experience this BSOD error while trying to install Windows 10, it will prompt you to restart your computer every single time you experience it. In most cases, you will also not be able to proceed with the Windows 10 set-up.
The “KMODE_EXCEPTION_NOT_HANDLED” error is normally caused by:
You won’t be able to successfully upgrade or set up Windows 10 if you continue to encounter this BSOD error. Note that this error will always prompt your computer to restart every time it happens, preventing you from completing the Windows 10 set-up.
If you’re not tech-savvy or not capable of debugging this issue, it’s highly advisable to proceed with the basic troubleshooting techniques available in this link.
After troubleshooting, below you’ll find a few solutions to rectify the issue.
Two common causes of the KMODE_EXCEPTION_NOT_HANDLED issue are hardware incompatibility and faulty device driver or system service.
If you experience this error, check first if any of your newly installed hardware is compatible with Windows 10. You can find the required hardware for Windows 10 from this link.
If all your hardware is compatible with Windows 10, you might need to check the device driver or system service. Review the bug check message. If any of the drivers you have is listed in the message, either disable or uninstall them before upgrading or setting up Windows 10.
You might also find it useful to check the System Log available in the Event Viewer for other error messages that can help you figure out the driver or device that’s causing the error. Running hardware diagnostics can also be useful.
Other troubleshooting steps include:
If you still experience the error after doing the methods above, you might want to try a powerful and trusted automated tool to fix the job.
Error code 0xc004fc03 occurs when Windows users fail to activate their Windows operating system due to a networking problem. The error code’s common symptoms include the following:
Error code 0xc004fc03 in Windows 10 usually occurs due to issues related to a Windows user’s network. Your computer may be having problems connecting to the Internet or your firewall may be blocking or interrupting your device’s ability to activate Windows 10. In some cases, users may simply need to wait a day or two to reattempt to activate their system using a valid product key, as there may be an issue with the Windows activation servers. Failure to promptly fix this error code might result in other Windows 10 error messages, such as error code 0xc004f034.
To rectify the error code, Windows 10 users will need to perform manual repair procedures that fix the underlying problems causing error code 0xc004fc03. These procedures may include reconnecting to one’s network, checking your firewall settings, or activating your Windows operating system via phone. The manual repair methods are simple and do not require technical knowledge of the Windows operating system. If your attempts at manually repairing this error code fail, however, you may need to try a few other procedures.
To check your Internet connection, you’ll need to access the Network & Internet tab in Windows 10. Follow the instructions below to access this tab and fix Internet connectivity issues if they are preventing you from activating Windows on your machine.
If your status shows that you are not connected to a network, you will need to fix your connection. Simply use the Network Troubleshooter to troubleshoot your connection. You will be able to activate your copy of Windows once your connectivity issues are resolved.
If, however, the problem persists and error code 0xc004fc03 occurs during the activation process, this simply means that the existence of the error code is not due to connectivity or networking problems. In such a case, move to the next manual repair method listed below and follow the exact instructions given.
Windows Firewall protects your PC from hackers, worms, and other malicious programs. However, in some cases, it may result in error codes like error code 0xc004fc03. If your firewall is interfering with the Windows 10 activation, you’ll be able to rectify the problem by simply adjusting your settings. Follow the steps below to check – and adjust if necessary – your Windows Firewall settings.
In some cases, Windows users may not be able to adjust settings within the Windows Firewall tab, as your firewall settings may be controlled by a third party antivirus software. If this is the case, open the antivirus software and turn off the firewall if the software does not prevent you from making such changes to its settings.
Note, however, that you will need to readjust the settings as soon as you activate your version of Windows 10. This is due to the fact that turning off your firewall settings permanently may lead to exposure to worms and other malicious programs.
Activation of Windows via phone is another option for individuals experiencing error code 0xc004fc03. The activate by phone option in the Update & Security tab will be available once you fail to activate Windows 10. To complete this manual repair method, follow the steps below.
This is one of the most effective ways to fix error code 0xc004fc03. If the issue persists, however, you can proceed to the last resort.
If you wish to always have at your disposal a utility tool to fix these Windows 8 and other related issues when they do arise, download and install a powerful automated tool.
FromDocToPDF Toolbar is a browser extension published by Mindspark InteractiveNetwork, that usually comes bundled with other potentially unwanted programs. The toolbar is distributed heavily through advertising networks.
This toolbar automatically sets your default search engine to MyWebSearch, it also sets your new tab to the DocToPDF welcome page. This toolbar ads startup registration tasks that allow it to start automatically with Windows, it gathers website traffic, clicks, data, and personal information and sends it to its ad network. Multiple anti-virus programs have detected FromDocToPDF as a browser hijacker and therefore is potentially unwanted and recommended for optional removal