Top 10 Worst Computer Viruses

The birth of the Morris Worm in 1988 sparked a new era of concern for computer security, marking the beginning of what would become a complex battleground between cybercriminals and cybersecurity professionals.

Computer viruses have evolved significantly over the years, moving far beyond simple pranks and moving into the realm of serious criminal activity and even international cyber warfare. From stealing personal and financial data to locking users out of their own files for a ransom, these digital bugs have become a major global concern.

What actually makes a virus successful, or should we say, effective? Well, there are a couple of factors. Stealth is key - the best viruses are often those that can infiltrate a system without detection, silently working in the background. They might exploit known vulnerabilities in software, or use social engineering tricks to get users to unintentionally download and execute them. Then, once they've set up shop in a system, they propagate. They spread as widely and quickly as possible, infecting other systems through networks, email attachments, or even USB drives.

But the worst viruses? They're not just stealthy and prolific, they're destructive too. They cause serious damage, whether that's wiping out critical system files, stealing sensitive data, or even recruiting the infected system into a botnet for use in larger scale cyber attacks.
The Top Ten
1 ILOVEYOU The ILOVEYOU virus, also known as "Love Bug," emerged in 2000 from the Philippines. This infamous worm was propagated through email, enticing recipients to open a "LOVE-LETTER-FOR-YOU" attachment, leading to system compromise and rapid replication to all contacts in the recipient's address book.

This virus has infected over 10 million computers since 2000. And what happened you may ask. You get a file named "LOVELETTER". You're computer gets infected. Pretty bad. It doesn't exist anymore. But people have reported it's still out there. If you get a file titled "LOVELETTER". Do not open it. Or you're infected

Thank GOD its not here. But legend has it that people have reported its still out there

If it were still here, this would be a nightmare!

2 Sasser Debuting in 2004, the Sasser worm exploited a vulnerability in non-updated Windows XP and 2000 systems. The virus could infect a system without user interaction, causing issues with system stability and network traffic due to its rapid replication capabilities.
3 CryptoLocker As one of the first widely known ransomware attacks, CryptoLocker emerged in 2013, encrypting victims' files and demanding a Bitcoin payment for their release. It was typically spread through infected email attachments and compromised websites.

Imagine someone barfing all over your xbox, then asking for $500 so they can clean it up LIGHTLY, and then does it again the next day.
That's CryptoLocker for you.

Ransomware in general is the worst - it honestly makes me vie for the days of fake antivirus programs.

Worst virus ever. It encrypts your computer's data, and demands a ransom of a high price to get it back. And even if you manage to delete the virus from Safe Mode or something, your files WILL STILL BE ENCRYPTED.

4 Code Red The Code Red worm surfaced in 2001, exploiting a buffer overflow vulnerability in Microsoft's Internet Information Services (IIS) web server. It defaced affected websites and used the compromised systems to conduct Distributed Denial of Service (DDoS) attacks.
5 CIH Virus Identified in 1998, the CIH Virus, also known as Chernobyl, is a destructive virus that can overwrite critical information on the system's BIOS chip, rendering the system unbootable. It is also capable of overwriting data on the user's hard drive.

An old virus that could destroy Windows and the first few sectors (Master Boot Record or Master File Table). Some certain variants can even destroy the BIOS and/or CMOS by overwriting it with random bytes of data - essentially making the computer a paperweight. Patched in BIOSes newer than 2001/2002, this virus is ancient by today's standards. The virus first emerged in 1998 and caused around $1 Billion US in damages, thought to infect over 60 Million machines worldwide. No one needs to worry about this virus these days, considering the fact that it only infects Windows 9x OSes (95, 98/98SE, ME), and is patched in any motherboard manufactured past 2002.

6 Morris Worm The Morris Worm was one of the first computer worms distributed via the Internet. Released in 1988 by Robert Tappan Morris, the worm exploited vulnerabilities in Unix systems and replicated so aggressively that it often caused systems to become unresponsive, marking an early example of a Denial of Service attack.

This virus spreaded so quickly that it had 10% of computer shut down at the time! It also took about 6 days to be removed from a computer. The way it worked was that it would replicate itself infinitly and move to other computers.

7 Reveton This notorious ransomware would "lock" users out of their computers, typically displaying a fraudulent message alleging the user's illicit activities and demanding payment under the guise of law enforcement agencies. First spotted in 2012, it has many variants including the FBI virus and Metropolitan Police virus.

This virus just the worst. After you watch something disgusting, listen to music on websites, or play violent games. You get a pop up saying your personal computer has been blocked, and they show screenshots and make you wonder "Wow. My actions can be watched and taken to the police." And it asks you to pay a fine of 200$ (Correct me if I'm wrong) and after it popped up. When you try to log into your computer. You get the virus page instead of the info. If you get this page, don't listen to it. It's just made by a homeless guy who tries to get money from you.

8 MEMZ Originating as a custom-made trojan for a YouTube series in 2016, MEMZ is known for its intense visual payload, causing graphical distortions, opening numerous browser tabs, and rendering the system unbootable. It's often found in malicious downloads masked as legitimate software.

Kills your computer, forever displaying a Nyan Cat...

9 PGPCoder Also known as GPCode, this was one of the earliest forms of ransomware. It surfaced in 2005 and encrypted a wide range of user files using RSA encryption, then demanded payment for the decryption key.
10 Stuxnet This sophisticated worm, discovered in 2010, specifically targeted supervisory control and data acquisition (SCADA) systems used in industrial applications. It's most well-known for disrupting Iran's nuclear enrichment program by causing centrifuges to spin out of control.
The Contenders
11 Zeus Identified in 2007, Zeus, also known as Zbot, is a Trojan horse primarily used to steal banking information by man-in-the-browser keystroke logging and form grabbing. It is often spread through phishing schemes or drive-by downloads.
12 Spora Emerging in early 2017, Spora is a sophisticated ransomware variant. Unlike most ransomware, it doesn't simply encrypt files; it also offers a range of "services" on its payment site, such as immunity from future attacks. Its name originates from the Russian word for "spore", reflecting its spread mechanism.
13 Melissa The Melissa virus is a macro virus that was spread via email attachments, appearing in 1999. It proliferated by sending itself to the first fifty contacts in a user's Microsoft Outlook address book, and could potentially disable safeguards in Microsoft Word and Outlook.
14 The Flame Worm Discovered in 2012, Flame (also known as Flamer or Skywiper) is an advanced persistent threat (APT). This modular malware targeted Middle Eastern countries and was used for cyber espionage, capable of recording audio, screenshots, keyboard activity, and network traffic.

'The most complex malware ever found.' Why is it not higher?

15 Pikachu Virus Named after the famous Pokémon character, this was the first virus aimed at children, appearing in 2000. Distributed via email with the subject "Pikachu Pokemon", when opened, it would attempt to delete key system files on reboot if the user activated the payload.

Shuts down your computer and ASKS you if you want to delete all your stuff

16 Mydoom First spotted in 2004, Mydoom (also known as Novarg) is a rapidly spreading email-based worm. At its peak, it was responsible for a significant percentage of all emails sent worldwide. The worm could open a backdoor on infected systems, allowing remote control.

Mydoom is most dangerous worm in all computer viruses. Mydoom was first sighted on January 26, 2004.

I wonder why this isn't higher on the list...

17 WannaCry This ransomware attack, occurring in May 2017, spread through a vulnerability in Windows' Server Message Block protocol. WannaCry encrypted users' files, demanding Bitcoin payments for their release, and affected numerous institutions worldwide, including the NHS in the UK.
18 Cerber Cerber, a ransomware-as-a-service (RaaS) that first emerged in 2016, is notable for its evasion techniques and voice-recorded ransom messages. It uses sophisticated encryption to lock users' files and demands a ransom to decrypt them.
19 Slammer Also known as Sapphire, Slammer is a worm that caused a dramatic denial of service on the internet within minutes of its release in 2003. It exploited a buffer overflow vulnerability in Microsoft's SQL Server and Desktop Engine database products.
20 Storm Worm Identified in 2007, the Storm Worm, also known as Nuwar, is a backdoor Trojan that was propagated through a deceptive email with a clickable link. When activated, it would turn the host computer into a botnet for sending spam or performing Distributed Denial of Service (DDoS) attacks.
21 Navashield Navashield is rogue antivirus software, masquerading as a security tool to trick users into purchasing its "full version" to remove non-existent threats. Notable for its aggressive and scaremongering tactics, it was first observed in 2007.

Look it up. Not popular, but if you got it on your computer, you would be screwed.

22 Nimda Named for "admin" spelled backward, Nimda is a file-infecting worm that surfaced in 2001. It spread rapidly, exploiting several known vulnerabilities and using various propagation methods, including email, open network shares, and compromised websites.
23 Magistr First appearing in 2001, the Magistr worm is infamous for its destructive payload, including the ability to delete critical system files and overwrite the BIOS. It typically spreads through infected email attachments and network shares.
24 Conficker Emerging in 2008, Conficker, also known as Downup or Downadup, is a worm that exploited weaknesses in Windows OS to create a botnet. It's one of the largest known botnets and can prevent system updates or installations of security software.
25 Abraxas The Abraxas virus is a JavaScript-based malware used primarily for cryptocurrency mining without the consent or knowledge of the affected user. Upon infecting a system, it uses computational resources to mine cryptocurrencies, often leading to system slowdowns.
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