While computer viruses are still not as dangerous as actual, real-life viruses, they can still cause a significant amount of damage if they’re left out in the open and allowed to infect a large number of computers – much like their natural counterparts. In the past few years, viruses and other similar types of mass cyber attacks have managed to cause a lot of real harm to people and businesses around the world, often in the form of loss of crucial data and financial damages.
10. Stuxnet
The Stuxnet worm was discovered on June 17, 2010 by an antivirus firm called VirusBlokAda. Widely considered one of the most sophisticated cyber weapons ever created, it was a malicious computer program that was designed to target industrial control systems, specifically those used in Iran’s nuclear program. The worm was able to infiltrate the country’s computer networks and spread rapidly due to its aggressive nature, soon spilling outside the borders of its intended target.
Stuxnet was a type of cyber attack known as a “worm,” which is able to self-replicate and spread from one computer to another without human intervention. In the case of Iran’s nuclear program, Stuxnet was specifically designed to target the centrifuges used to enrich uranium, causing them to malfunction. According to reports, the worm was successful in infecting thousands of computers, along with setting Iran’s nuclear program by several years, especially due to its sabotage of the systems at the Natanz nuclear facility.
9. MyDoom
MyDoom, also known as Novarg, is a malicious computer program discovered in January 2004. It’s a worm-type virus that spreads through email attachments, file-sharing networks, and other channels. Once a computer is infected, MyDoom can use it to send out spam emails, launch denial-of-service attacks, and collect sensitive information, among a bunch of other harmful applications.
MyDoom usually arrives in emails with subject lines that appear legitimate, often tricking users into downloading and running the malicious code. It caused quite a bit of damage and disruption in its early days, infecting millions of systems and causing about $38 billion in damages.
MyDoom was also responsible for a number of high-profile denial-of-service attacks, including the one against Microsoft, resulting in their websites being unavailable for several days. According to one estimate, the virus infected about 1 in 12 emails at its peak, making it one of the largest cyber attacks in history.
8. Klez
The Klez virus was a mass-mailing worm first detected in December, 2001. Its first variant was capable of spreading through email attachments and Internet Explorer, primarily affecting computers running Microsoft Windows. Since then, multiple, advanced variants have been discovered, including ones that can easily spoof email addresses from authentic sources.
The Klez virus and its variants are particularly dangerous due to their ability to modify or delete files on an infected computer. It can also steal email addresses and passwords, making it a major threat to the data stored by personal and business computer users. Some Klez versions are even capable of disabling antivirus software and creating backdoors for hackers to gain access to the machine, leading to more serious crimes. The Klez virus caused global damage in the early 2000s, as it infected millions of computers and email servers worldwide.
7. SoBig
The Sobig virus first started infecting computers in 2003. It was a kind of a computer worm that used email and shared network folders to spread rapidly to other computers. Sobig even had the ability to create its own server, allowing it to send out infected emails to thousands of users without a host email account. At the time, it was also called the fastest e-mail virus outbreak in history, far surpassing the previous record held by Klez.
Sobig specifically targets computers running on Microsoft Windows. Much like other successful viruses, it uses the tried-and-tested email network to spread around, specifically email attachments. At its peak, more than 1 million copies of Sobig were found in emails around the world, as reported by a digital security firm called MessageLabs Inc. Apart from causing real-life financial losses, the virus also had an immeasurable impact on people that lost valuable data or documents in the attack.
6. Zeus
Zeus was a type of Trojan virus first discovered during a cyber attack against the United States Department of Transportation. It’s a financial or banking virus, designed to steal sensitive information from infected computers like banking credentials, credit card numbers, and other personal details. While it could pass around in a number of ways, the Zeus Trojan primarily spread through email attachments, malicious downloads, or vulnerabilities in web browsers and other online software.
Zeus can remain hidden and undetected for long periods of time, as it gets lodged in a computer or security system and continuously captures sensitive data to send it back to the attackers. Later variants were even capable of keylogging, taking screenshots, and stealing login credentials from user activity. Zeus has been known to target financial institutions, government agencies, and corporations, making it a significant threat to everyday users and large organizations alike.
5. CryptoLocker
CryptoLocker is now a fairly well-known type of malware that encrypts a victim’s files and demands payment in exchange for the decryption key, or some other variation of it. It can spread in a variety of ways, typically email attachments, file-sharing sites, and downloads. CryptoLocker primarily targets Windows users and has been known to rapidly spread across networks if left unchecked.
Once installed on a victim’s computer, the malware encrypts files using a strong encryption algorithm, making them inaccessible without a password or key only known to the hacker. They then demand payment in exchange, usually in the form of Bitcoin or other cryptocurrencies. Depending on the victim and attacker, the ransom could range from a few hundred to several thousand dollars.
CryptoLocker is what we know as ransomware – a specific type of malware that causes damages worth billions of dollars around the world every year. It can even shut down systems critical for public safety and well-being, like hospitals and government agencies, until a ransom is paid out, making it all the more dangerous in the larger scheme of things.
4. PlugX
PlugX is a type of Remote Access Trojan (RAT) used by cybercriminals for a specific type of cyber attack known as an Advanced Persistent threat (APT) attack. RATs are malicious software that give attackers remote access to a victim’s computer, allowing them to control it like they were physically there. PlugX is typically delivered through targeted phishing emails or software vulnerabilities. Once installed, it can give attackers complete control over an infected system, allowing them to steal data, execute commands, and install additional malware.
PlugX has been linked with the military, as it has been used in targeted attacks against government agencies, defense contractors, and other high-value targets. It’s particularly effective at evading detection by security software, as it can remain undetected on a compromised system for long periods of time. Once an attacker gains access, they can use PlugX to attack the machine itself, or infect it and use it as a jumping-off point to other, more important systems on a network.
3. NIMDA
The Nimda virus was first detected in September 2001. It’s a sophisticated piece of code that spreads through multiple attack routes, including email, websites, and network shares. The virus combines the best techniques used in worms, viruses, and Trojan horse kind of attacks, and was capable of infecting both servers and workstations running on Microsoft Windows.
The Nimda virus has so far caused hundreds of millions in damages, as it can easily spread through features we use every day, like email attachments. Unlike other viruses, Nimda didn’t seek to cause harm to the files or network security of systems. It went for the more delayed, chaotic effect by slowing down the entire network for extended periods of time, usually by sophisticated denial-of-service attacks. Nimda is also capable of exploiting known vulnerabilities in web servers, allowing it to infect a large number of computers in a short period of time.
2. Fizzer
The Fizzer worm was first detected in 2003 by the antivirus firm Kaspersky Labs. It’s a complex and sophisticated malware, with the ability to spread through multiple channels like email, instant messaging, and file-sharing networks. When it was first discovered, Fizzer was rapidly spreading through the Kazaa network, as it infected a large number of computers before it could be found.
Once installed on a computer, the Fizzer virus can perform a wide range of malicious actions, like stealing passwords, credit card numbers, and personal data, along with disabling security software to open backdoors for more advanced actions. Some versions have even been known to send infected emails to the victim’s contacts, increasing the likelihood of further infection to other systems. Fizzer remains one of the most widespread viruses in the world, even if it’s no longer as effective as it used to be back when P2P file-sharing was still popular.
1. Sircam
The Sircam worm was discovered in July 2001, and it quickly became one of the most widespread and damaging computer viruses of all time. It was designed to primarily spread through email and network shares, using a variety of tricks to lure users into opening infected email attachments. Once installed on a system, the worm would attempt to spread to other computers on the same network, combined with malicious actions like deleting files and sending itself to all the contacts in the user’s email address book.
Sircam caused billions in damages and infected millions of computers worldwide, largely due to its resilience and highly-infectious nature, as it was difficult to detect and remove in many cases. At its peak, Sircam accounted for a large percentage of virus infections online, making it one of the largest security threats ever. Thankfully, Sircam is no longer as active as it once used to be, though it remains a threat for certain legacy Microsoft operating systems still in use for specific purposes.