5 Worst Computer Viruses of All Time

Frustrated Woman at Computer With Stack of Paper
Frustrated Woman at Computer With Stack of Paper


A computer Virus is a kind of malware that can replicates itself and infect other files in a computer. In part where the virus replicate is known as infected area. Virus often perform many harmful activities like stealing space in hard disk, accessing private information, running random program, displaying messages and logging keystrokes.

Computer viruses are not a new invention, it have been around for many years. Earlier days of computer, von Neuman also talked about a self-replicating program. But he never knew that these programs will be the main arm of hackers. Virus programs are written by hackers to harm systems of an organization or common people. This can be for business or fun.

In past few years, millions of computer viruses have been identified by researchers. But there are few computer viruses which were able to write their name in the history of computer. In this post, I am listing 5 worst computer viruses of all time in history. You must read this post to know about worst computer virus.

Computer Virus

Worst Computer Viruses of All Time

1. Melissa

Melissa was created by David L. Smith in 1999. This computer virus was based on the computer Macro. Smith has created this virus to spread via email messages automatically. The virus was based on Microsoft Word macro. Melissa sends an email to a person and ask him to open a secret document attached in the email. Once the recipient open the document, this virus sends itself to top 50 people in the email address book of the victim.

Melisa Virus

In few days, this virus was transmitting on internet. The increase in email traffic due to this virus forced many companies to stop their e-mail programs. The damage caused by the virus was estimated at more than $100 million.

Smith was caught and then sent to 20 months jail. He was also fined $5,000. Court also ordered him not to access any kind of network or internet without court’s permission.

2. I Love You

“I Love You,” a virus with interesting name, was emerged from Philippines. This was much powerful the Melissa and was capable of replicating itself. It traveled across millions of computer by email with a message line of “Love Letter from a secret Admirer.”Email also had a attachment (LOVE-LETTER-FOR-YOU.TXT.vbs) that created lots of trouble to users. As the name suggest, it was a visual basic file that was capable of doing these things.

  • Copy itself several times and hide copies in several folders in system
  • Add New keys in system registry
  • Download a file from Internet. This file was actually a remote keylogger to steal passwords and sent to hacker.
  • Spread itself via email and Relay Chat clients.

Sources confirmed that this virus caused $10 billion damage.

3. Klez

Klez was another popular computer virus that created lots of trouble to Internet users back in 2001. It also had several variations on the Internet. Basic Klez worm infect a system via email message. It was able to replicate itself and send its own copies to victim’s contacts via emails. It was also able to disable virus scanners and virus removal tools.

Klez worm

Few variations of this work could also act like dangerous Trojan.

It exploited the vulnerability of Internet explorer’s Trident rendering agent. This agent was also used in Outlook, to Outlook users were also affected by this.

4. SQL Slammer/Sapphire

SQL Slammer or Sapphire targeted Microsoft SQL Servers and Desktop Engine database software. It targeted many computer networks in January 2003 and brought down many server systems. Bank of America’s ATM service was crashed due to this virus. Many other popular services were also crashed including 911 service and Continental Airlines.

This virus was too fast. Only in few minutes after infecting fist computer service, it began doubling the number of victim’s per second. It just 15 minutes, it crashed almost half of the major computer services of the internet.

Reports claims that SQL Slammer caused more than $1 billion in damage.

5. Sasser and Netsky

Sasser and Netsky was two popular computer viruses developed by a 17 years old German hacker Sven Jaschan. These programs were created in different ways to perform different tasks.

Sasser was a computer worm created to infect Microsoft Windows vulnerability. It looked a victim by scanning IP for a random IP address. In this way, it started infecting various computers on Internet. It also altered systems in a way to make hard to shutdown a computer. Users needed to cut the power to turn off the system.

Netsky virus started infecting computers via emails. It spoofs email address and propagates through a 22,016-byte file attachment.

Sven Jaschan was caught but didn’t spend time in Jail because he was under 18. He only received a sentence of one year and nine months of probation.

There are many other popular worst viruses including Storm Worm, MyDoom, Nimda, Leap-A/Oompa-A and Storm Worm.