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 historyIn 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.
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
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.

10 worst computer viruses in history“Fatal error, Installation fails, Installation ended prematurely because of an error”.Moreover, this kind of error is a generic one that can also occur with any software reinstallation or installation. And to fix this error, there are several suggestions you must check out. You can try to install or reinstall the program in a Clean Boot State or restart the Windows Installer Service. You could also try to re-register the Windows Installer Service or re-register the VBScript.dll file.
Error code 10 is a type of Window Device Manager error code. This error code is generated when the Device Manager can’t start the hardware device or is experiencing device driver issues. It is displayed in the following format:
"This device cannot start. (Code 10)"
You can access complete details about error codes related to Device Manager such as code 10 through the Device Status area in the Device Properties.
By accessing Device Status, you can easily view the status of each device and learn about the specific device that could be causing the problem.
Error CausesError code 10 can be triggered due to several reasons. These include:
Device driver corruption can cause you great inconvenience and PC performance issues. The computer’s operating system relies heavily on device drivers to communicate with the hardware.
For example, the printer driver facilitates functioning of the printer. Similarly, the graphic card driver ensures proper video output on the monitor screen.
However, your PC hardware, such as printer or keyboard, may stop functioning properly if their device drivers become outdated or corrupt. Therefore to avoid inconvenience and to ensure your PC works properly, it is important to resolve the problem immediately without any delay.
To repair error code 10, you don’t have to be a technical whiz or hire a professional computer programmer. Here are some of the best and easy to perform DIY methods that can help you fix this device error in no time.
Sometimes temporary problems in Device Manager can also generate code 10 error. Therefore it is advisable to restart your PC. Rebooting your system might fix the error. Try it! If it does, great, however, if the error still persists, then try other methods listed below.
Go through the Device Status in the Device Properties to view the driver causing the problem. If any driver is tagged with a yellow exclamation point, it means that driver is the one causing problems. Once identified, uninstall that driver and then reinstall it. This will hopefully resolve the problem.
Whether the error code 10 is generated due to incompatible, corrupted, or outdated device drivers, simply update the device driver to resolve. To update the driver, go to the Device Manager, then click the driver tab in the device properties dialog box.
After that, click update driver. This will start the hardware update wizard. Then follow the instructions to update the driver on your PC. During this process, you may be prompted to provide the driver path.
If you don’t have it, then you will have to download the latest driver from the hardware vendor’s official website. This can be time-consuming and stressful.
Another alternative is to install DriverFIX. It is a user-friendly device driver management software with an intuitive interface.
Its intelligent algorithm is designed to detect all the problematic drivers in seconds. It automatically updates and accurately installs appropriate drivers and ensures your PC runs at its optimum level in no time.
Click here to download DriverFIX on your system to resolve error code 10.
Users, when upgrading to Windows 10 from Windows 7 or Windows 8/8.1, or when upgrading to a new version, build, service pack, or major update of Windows 10, can encounter error code 0xC1900101, 0x30018. Windows 10 installation fails and stops or hangs. During the installation process, it will reach a certain maximum limit (normally at 6% or 32%) then reverts back to the previous version of the operating system and displays the following message:
We couldn’t install Windows 10. We’ve set your PC back to the way it was right before you started installing Windows 10.
0xC1900101 – 0x30018 The installation failed in the FIRST_BOOT phase with the error during the SYSPREP operation.
Error CausesIn attempting to fix Error Code 0xC1900101-0x30018, it is vital to know what causes this issue. The most probable causes of this error are:
NOTE: If this fails, if possible, you can try using the .ISO file in upgrading.
If you’re using Windows Update in installing Windows 10, you can implement the following:
NOTE: Don’t forget to hit Enter after every command.
net stop wuauserv
net stop cryptSvc
net stop bits
net stop msiserver
NOTE: Don’t forget to hit Enter after every command.
ren
C:WindowsSoftwareDistribution SoftwareDistribution.old
ren
C:WindowsSystem32catroot2 Catroot2.old
NOTE: Don’t forget to hit Enter after every command.
net start wuauserv
net start cryptSvc
net start bits
net start msiserver