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The loading procedures are sluggish. The alerts from your anti-virus program. When friends email you to let you know something is wrong. The spam. The odd answers. Death’s blue screen. Viruses have existed for as long as personal computers, and they are a major problem because they seriously impair computer performance. The viruses are more sophisticated than our tools for detecting and preventing them. Consequently, knowing what is a computer virus is very important for businesses or even individuals in 2025.

When you come across one of these viruses on your computer, sometimes even the strongest defense cannot keep it secure. Since they may erase your valuable data at any time and cause your computer to operate strangely, the most dangerous virus for computer has served as a serious concern to computer users for many years.

We now know otherwise; their growing prevalence has coincided with their potential for damage. From Conficker, which had infected around 15 million machines and had created confusion and fear, to Slammer, which nearly caused damage worth $10 billion, they are now spreading throughout the world at the speed of light.

Keep reading and exploring to learn what are the worst computer viruses in the history and are there viruses written in forth or not in 2025.

What is a Computer Virus?

System disruption, significant operational problems, and data loss and leaks are the goals of computer viruses. It’s important to understand that computer viruses propagate via systems and computer applications. When a computer virus attaches itself to an executable host file, its viral codes start to run when you open files. The code then propagates over disks, networks, file-sharing applications, or malicious email attachments from the software or document to which has attachment.

Virus protection is crucial, but what is a computer virus and what are the worst computer viruses? A most dangerous virus for computer will almost always negatively impact the device it infects. Moreover, you may identity it by typical symptoms of weak performance, such as:

1. Internet Latency
2. Windows that pop up
3. Self-executing programs
4. Logging out of accounts
5. Device crash
6. Your email account is sending a lot of emails.
7. Modifications to your main page

Not every computer virus personified has the intent to damage the hardware, software, or data on your computer. On the other hand, the majority of computer viruses are malevolent and carry out harmful tasks, such as erasing files and data. While some famous computer viruses remain dormant until a particular event triggers the execution of their code on a computer, others can create havoc when their code is executed.

What Are The 20 Most Famous Computer Viruses?

Let’s discuss what are the worst computer viruses that cost companies billions of dollars.

ILOVEYOU

Among the history of computer viruses, the ILOVEYOU worm stands apart because of the great damage malware might produce. By hiding as a love letter and sending through email attachments, this malevolent virus fooled careless users into activating it. Personal information was deleted and large financial losses resulted when the virus’s destructive payload was released during its execution. This notorious viral strain is proof of the strength and potential for mayhem that famous computer viruses possess.

Also Read: 20 Examples Of Web Browser: A Tour Of The Browser Landscape

CryptoLocker

If you want to know about what is a computer virus, CryptoLocker is the one you must study in 2025. In September 2013, by using fake email attachments to covertly infiltrate systems, it encrypted valuable data and effectively held them ransom. The makers of CryptoLocker compelled hundreds of thousands of victims to pay ransoms to get the decryption key. This crucial incident brought to light the danger and profitable nature of ransomware attacks, emphasizing how crucial strong types of cybersecurity protections are.

Mydoom (2004)

Mydoom propagated more quickly than any previous virus. It infected PCs via peer-to-peer file sharing and email. Once inside, it gave hackers a “backdoor.”

It includes:

• Start strong DDoS assaults.
• Take advantage of email addresses.
• Cause damages exceeding $38 billion.

Hackers frequently use backdoors to take control of compromised machines. You may avoid this kind of computer virus by blocking unfamiliar apps and maintaining system updates.

Pikachu

Additionally, the first most dangerous virus for computer that specifically targeted children was launched in 2000. An email containing the Pokémon character Pikachu had created the Pikachu virus. “Pikachu is your friend” was the subject line of the email. The file was actually a picture of the Pokémon, but it actually has a Visual Basic 6 application which was pikachupokemon.exe that had erased folders’ contents. Thankfully, the possible harm was limited by a notice regarding the deletion.

Melissa

First discovered in March 1999, the Melissa virus spread to the general public through emails and online forums that provided free login information for pornographic websites. The virus was distributed via a Microsoft Word document that had an embedded macro that would execute malicious code when it was opened. Therefore, you must learn what is a computer virus and types first. Melissa propagated itself to the first 50 contacts in a user’s Outlook address book if macros were enabled. Infected devices reported slowdowns and bulk mailings. According to forensic assessments, the cost of recovering from the worldwide attack was at least $80 million.

Also Read: Cyber Security Tools: 30 Essential Solutions For Maximum Protection in 2025

Sobig

Please pardon the pun, but Sobig’s harm was enormous, amounting to $30 billion. Similar to Mydoom, spam emails were used to propagate Sobig. Its indiscriminate nature made it far more damaging, and unlike Mydoom, it had no targeted targets.

It jammed and shut down the email system at MIT, yes, Massachusetts Institute of Technology, whose Electrical Engineering & Computer Science program is the largest and popular undergraduate program. This occurred during the height of its transmission, which coincided with the spread of the Sobig.F version.

Storm Worm

Storm Worm, a most dangerous virus for computer that set itself apart with a menacingly dishonest strategy, emerged in the cyberthreat arena in 2006. By using the headline, “230 dead as storm batters Europe,” the virus was able to attract inquisitive minds.

The virus was activated by merely clicking on a link in the email, and it then seized control of computers, transforming them into bots that increased the infection’s dissemination and produced enormous volumes of spam. The Storm Worm, also known as the Storm Bot, disrupted the digital world by infecting millions of emails.

Sircam

Emails on Microsoft Windows systems were used to disseminate the Sircam worm later that year, in July 2001, and the infection was transferred among computers via the network. A mass-mailing worm called Sircam can spread over Windows network sharing. When an EXE extension file executes, this worm starts to run until it has done so 8000 times. This also the latest computer virus in our what is a computer virus guide.

Code Red Worm

A Code Red worm was discovered on the Internet on July 15, 2001. It targeted PCs running Microsoft’s IIS web server. Following Sircam, Code Red launched an assault against Microsoft’s Internet Information Services’ Index Server ISAPI Extension.

Code Red II

A few weeks later, Code Red II came to the world when someone had modified the original Code Red worm, not to become outdone. Millions of devices were infected by the new, far more aggressive variant, which had a significant impact in China.

The SQL Slammer

The SQL Slammer worm, also known as the Sapphire worm or the Helkern worm, appeared in January 2003. It targeted MSDE and Microsoft SQL Server. The worm became the fastest-spreading worm ever because it was able to exploit weaknesses so rapidly. After the first victim was targeted, internet connectivity was disrupted globally within fifteen minutes. SQL Slammer may cause your overall internet traffic to lag.

Sasser & Netsky

Sasser and Netsky, two separate but related famous computer viruses created by a 17-year-old German student called Sven Jaschan, told a story of youth and upheaval. While Netsky spread via email channels, Sasser’s strategy was purely on scanning random IP addresses. Damage from this twin threat totaled billions of dollars. Although Jaschan’s intentions for creating these infections are indefinite, it’s possible that she had wanted to surpass even the infamous MyDoom malware.

Anna Kournikova Worm

Named after the well-known tennis star, the Anna Kournikova worm took advantage of her notoriety to deceive unsuspecting victims. The innocuous-looking subject line, “Here you have, 0,” convinced the recipients to open an attachment containing a malicious file. The virus is the handiwork of a 20-year old Dutch boy, Jan De Wit, and it reflects the fascination of mischief that computer viruses could inspire. Even if the amount of damage was only about $166,000, the Anna Kournikova worm is nonetheless a noteworthy illustration of digital disruption. Therefore, learning what is a computer virus is necessary in 2025.

Zeus

Zeus is a Trojan horse that hackers use to steal bank account information and passwords, among other private financial information. It was initially identified in 2007 and connected compromised devices to a botnet, which is a vast network of computers under hacker control. Moreover, from the bank and other organizations, money was stolen using this botnet. Similarly, it was a estimate that the Zeus Trojan has caused direct financial harm of about $70 million. Moroever, experts believe that recovery costs for this would become much greater.

Also Read: Cyber Security vs Ethical Hacking: What’s The Real Difference?

The Stuxnet

Stuxnet is a computer worm that was primarily employed in cyberwarfare and was discovered in 2010. It spreads through damaged USB sticks. Industrial control systems used to manage nuclear power stations and other industrial facilities were the focus of the virus.

Because Stuxnet was so strong, it could physically harm Iran and control its nuclear centrifuges. Even though Stuxnet did not cause as much damage as previous viruses, it demonstrated how advanced malware may physically interfere with vital infrastructure.

WannaCry

WannaCry is also the most dangerous virus for computer  in 21^st century. It encrypts files on computer machines and demand payment from its victims, just like the majority of ransomware. The virus was distinct, though, in that it took advantage of flaws in out-of-date Windows operating systems to propagate quickly over computer networks.

The ransomware damaged large organizations and healthcare facilities to the tune of billions of dollars, infecting over 230,000 machines across more than 150 nations. Over $4 billion has been reported to have been lost financially as a result of WannaCry, and new ransomware strains are continually being created using its code. If you want to understand what is a computer virus, WannaCry is the best and the latest computer virus to study.

Witty Worm

The Witty worm, another record-breaking worm, first surfaced in March 2004. This worm exploited flaws in products made by Internet Security Systems. The first internet worm with a harmful payload was this one. Using a pre-populated group of ground-zero hosts, it propagated swiftly.

Sasser

The Sasser worm affected networks in the spring of 2004. The Windows LSASS service has flaws that this worm took advantage of. When the Sasser worm struck immediately after or in proximity to the MyDoom and Bagle versions, it was very effective. Sasser even had a reputation for closing companies.

Petya and NotPetya (2016–2017)

The malware Petya targeted the Windows machines’ boot sequence. A much more deadly variant was NotPetya.

NotPetya:

• Although it appears like ransomware, the files were permanently deleted.
• Strike big businesses like FedEx, Merck, and Maersk.
• It caused damages totaling more than $10 billion worldwide.

If you do not train your workers to spot malicious emails or downloads, even businesses with robust IT systems may fail.

Torpig

Torpig, often referred to as Sinowal and Mebroot, launched an attack against Windows computers in 2008. The Trojan disables anti-virus software, creating opportunities for hackers to get access to the user’s computer and steal data, install further malware, and alter files and data.

The Trojan-type software known as Torpig targets users of Microsoft Windows. However, this malicious malware inoculates a component that functions as a keyboard logger, as demonstrated by the research. Additionally, it may download and run a variety of files that infect computers with malware.

Conclusion

In this blog, we’ve discussed what is a computer virus and what are the worst computer viruses since 1999. Moreover, you can get rid of a variety of PC infections and worms using SSL certificate services (Symantec, GeoTrust, RapidSSL, Thawte, and Comodo). Avoiding computer viruses requires careful safeguards; otherwise, you risk serious issues.

With the aid of the knowledge in this blog, you can identify and remove famous computer viruses from your computer before they seriously damage your data or equipment. Comment below your queries if you still have any about computer virus and types.

FAQs (Frequently Asked Questions)

What is a Computer Virus In Short Answer?

A computer virus is a form of malicious software, sometimes malware, that attaches itself to trustworthy files or programs and multiplies itself to infect further systems. It needs a human action, like opening an infected file, to propagate.

How Do You Get Rid Of A Computer Virus?

To eliminate a computer infection, turn off the internet, enter Safe Mode, and do a trustworthy anti-virus and anti-malware scan to identify and eliminate dangers. However, after removal, install the latest operating system and anti-virus software, remove any suspicious apps or browser extensions, and clear the cache in your browser.

What Are 7 Types Of Computer Viruses?

7 types of Computer Viruses include:

1. Boot Sector Virus
2. Web Scripting Virus
3. Browser Hijacker
4. Resident Virus
5. Direct Action Virus
6. Polymorphic Virus
7. File Infector Virus

How Does A Virus Get Into A Computer?

A virus enters a computer by taking advantage of human involvement, such as opening malicious downloads, clicking on malicious email attachments, visiting hacked websites, or using infected USB sticks.