The Most Dangerous Computer Viruses in History

The most deadly computer viruses in history have destroyed computers worldwide, costing billions of dollars in damage. Some even threatened nuclear power plants and hospitals with ransomware attacks.

Thankfully, most of these outdated infections have been eradicated; however, some malware remains active today. If you want to keep your systems secure from potential threats, here are a few tips on how to stay ahead of them:

Brain Virus (1986)

In January 1986, two computer programmers from Lahore in Pakistan created what is widely considered to be the first computer virus: Brain. Dubbed Boot Sector Virus 1, this boot sector virus infected boot sectors on floppy disks and then spread throughout memory of those affected by it.

The virus worked by checking the most significant bit of a BIOS drive number being accessed and infecting any file with that bit set. This bit-checking code was fundamental to most computer viruses at that time.

Though not the first virus ever created, it certainly was one of the most successful. Its ripple effect spread around the world and inspired millions of anti-virus programs to be created.

What’s more, this was the first instance of a stealth virus that managed to bypass traditional antivirus software and reach its target. It managed to infiltrate through incompatibilities with certain drivers or an accidental use of certain registry keys.

It wasn’t until 1988 that a virus unleashed unprecedented destruction on the internet. The most remarkable feature of this worm was its capacity for replication and spread from machine to machine, causing more destruction than just regular malware could. Estimates for clean-up costs were in the multimillions, as were losses incurred by businesses and individuals who found their files damaged or unable to access their data.

Mydoom (2004)

Mydoom (2004) is a computer worm spread via email attachment. It was first identified in 2004 and caused major slowdowns in internet traffic as it spread through infected computers. Furthermore, Mydoom spreads via Kazaa peer-to-peer file sharing application, sending multiple copies of itself as email attachments to other users.

MyDoom was the fastest-spreading email worm in history when it was first identified on January 26, 2004, causing global Internet speeds to slow by around 10%. As a result, MyDoom has been widely blamed for numerous issues like slow page load times and loss of productivity.

At first, it was believed that MyDoom had been created by a Linux or open-source advocate in response to SCO Group’s legal actions and public statements against Linux. However, security researchers have since dispelled this theory and attribute the malware to organized online crime gangs.

The virus was primarily spread via email, appearing as an error with subject lines such as “error”, “mail transaction failed”, “test” or “mail delivery system” in different languages. It had the capability of infecting computers running unpatched versions of Microsoft Windows.

MyDoom not only sent a backdoor Trojan, but it had the capability to execute Distributed Denial of Service (DDoS) attacks as well. As such, MyDoom was one of the most destructive viruses in history.

Email attachments spread the infection, infecting both Windows and Macintosh computers. It has the capability to spoof an email address, sending return emails to third parties. Once installed, a backdoor Trojan allows unauthorized access to an infected machine as well as copying itself onto P2P networks for further spread.

In July 2004, Mydoom attacked Google, Lycos and Altavista with the goal of taking down the search engine for one day and slowing down internet traffic.

Sobig (2001)

The internet plays an integral role in our lives, so it’s essential to keep your computer secure. Viruses are particularly hazardous as they can destroy or freeze data, disable hardware and disrupt your internet connection.

Many viruses exist today, some of which have caused billions of dollars worth of damages. Some, like Sobig (2001), are notoriously hard to catch while others like Mydoom (2004) have been around for years and continue to cause havoc on millions of computers worldwide.

Before becoming infected, it is essential to comprehend how viruses operate. A virus can enter your computer by exploiting a flaw in its software and running malicious code on it.

During this process, it can steal private information from you or infect your data with viruses. Some viruses may also cause your computer to run slowly or stop working altogether.

Other viruses can be employed in Distributed Denial of Service attacks, which cause servers or websites to go offline. Such incidents have the potential to harm a company’s reputation or even take it offline completely.

Another way a computer virus can be used against you is to encrypt and hold onto your data – known as ransomware. This type of attack prevents access to your information, requiring payment in order to unlock it.

It is essential to know that you can safeguard yourself against these attacks by installing reliable antivirus software and keeping your computers up-to-date with the latest patches. Furthermore, you can utilize your internet browser’s settings to block suspicious websites and avoid opening email attachments from unknown senders.

Klez (2001)

Computer viruses are an unfortunately common issue, but they can be highly destructive. Not only do they steal data from computers and disrupt business operations, but they may also cause productivity loss as well as reputational harm.

In 2001, one of the most destructive worms in Internet history struck, causing millions of dollars in damages. Klez was a Windows-based virus that spread via email using security vulnerabilities in Internet Explorer and Outlook.

Klez was an especially dangerous computer virus because it could send itself randomly selected addresses on infected machines, making detection very difficult. Furthermore, it employed high stealth technology which meant most anti-virus programs failed to detect it.

The Klez worm was the leading security threat of 2001, infecting over 98% of all reported infections that year. It spread through Windows network shares and emails, with its powerful engines capable of sending out thousands of messages per second.

In 2001, the Sircam worm emerged and spread through emails and network shares on Microsoft Windows systems. This malicious computer virus took advantage of a vulnerability in Microsoft Outlook by sending itself out to random email addresses from an infected machine’s address book.

This virus was highly successful and caused significant financial harm to businesses and organizations worldwide. It infected over 500,000 machines worldwide, stealing information from over 200,000 computers and damaging over 4000 bank accounts.

Another worm that caused widespread destruction was Mydoom, released in 2004. This virus spread via mass emailing and infected millions of computers within hours. Furthermore, it could use an infected machine to launch Distributed Denial of Service (DDoS) attacks against other servers.