From ILOVEYOU to Heartbleed, here we have compiled the worst computer viruses that took down the digital world.

Over 2, 30,000 computers have been infected by WannaCry so far.

The list of WannaCry’s victim includes several major companies and government offices including Fedex, NHS, Chinese Universities and Nissan Motor Manufacturing. Counted among one of the malicious ransomwares, WannaCry “locks people out of their computer files until they pay a ransom to the hackers.”

Before WannaCry, there are many viruses (or bugs) that created havoc and sent the world into “disaster” recovery mode. They caused billion dollars in damage and affected real life infrastructure. Here we have listed such computer viruses.


ILOVEYOU or Love Letter is considered as one of the deadliest computer viruses. The virus was come into existence in May, 2000 and was created by two Filipino programmers, R. Ramones and O. Guzman in VB script. The virus was sent around in an email which subject line read “I Love You.” On being opened by a user, the virus overwrote system files and created copies to be delivered via MS outlook to all addresses in the address books.

The virus infected millions of computers worldwide, especially those having Windows OS, causing damages worth $10 billion. It was so dangerous that many large businesses and governments had to opt for offline mailing system to avoid getting infected.

Code Red

Code Red hit the Internet on July 15, 2001 and targeted the PCs being operated on MS IIS web server. It infected nearly 2 million servers out of 6 million IIS servers at the time, making it one of the worst computer viruses ever.

It capitalized on the vulnerability of bugger overflow issues in the PC, meaning that when a system receives more info than its buffer can accommodate, it starts overwriting adjacent memory. Once entered in the system, it used to create multiple copies of itself, consuming lot of resources in the system.

It was discovered by Marc Maiffret and Ryan Permeh, employees at eEye Digital Security. They called it Code Red because they were having Code Red Mountain Dew when they found the virus.

The Klez Virus

Klez virus started infecting the web world in late 2001. The virus was sent through an e-mail to the user’s system, where it duplicated itself into multiple copies and chose random e-mail addresses from victim’s address book to access other users’ system. The virus is notable for many things, for example, it could create the fake email address for the “FROM” (sender) line. It was so infectious that it could plague the user’s system from previewing or opening the message without downloading or executing the attachment. It is believed that the virus has caused nearly $19.8 billion in damage.

Storm Worm

Storm Worm popped up in January 2007 and attacked many computers using an email with a subject line said, “230 dead as storm batters Europe.”

Victims would open the mail and click on a malicious link to access the news. In this way, they were trapped by this virus. It was basically a Trojan horse that turned infected PCs into zombies or bots to deliver a huge amount of malicious mail. The virus was discovered in over 200 million mails by July 2007.


Also termed as Downup or Downadup, Conficker is a worm made its debut in 2008. It executed the flaws in MS Windows OS to infect the system. The worm would then change account lockout policies, cut off the access to Windows update and antivirus websites, and turn off several services. Then it would turn the computer into a botnet slave by installing certain software to get ransom from the user.

Conficker has infected nearly 15 million MS server system running on Windows 2000 and Windows 7 Beta all around the world. It has caused an estimate damage of $9 billion.


It was created by computer science student Sven Jaschan in 2004. The virus used buffer overflow vulnerability in Local Security Authority Subsystem Service (LSASS). Besides, the virus would capitalize the system resources to spread itself to other systems through the Internet and plague other automatically.


Heartbleed is a security bug that was discovered in April 2014. It is a serious threat present in OpenSSL cryptographic software library. This vulnerability made it easy to steal the information in any condition, by the SSL/TLS encryption used to protect the Internet. SSL/TLS are used to create secure environment over the Internet for applications like web, email, and messaging. The Heartbleed bug lets anyone on the Internet to encrypt the information being protected by the dated versions of OpenSSL software. It leads to the encryption of the traffic, the names and passwords of the users and the actual content.

So these are the worst computer viruses that shocked the digital world. Sooner or later, your PC may be on the radar of these deadliest viruses if you are not serious about cyber security. Therefore, consider updating your software from time to time and use the reliable antivirus software.

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