Deadlist Computer Viruses

 A computer virus is malicious code/program written to affect the operation of a computer. Like a biological virus, it is capable of reproducing and spreading from one system to another. It works by attaching itself to a legitimate program or document. Interestingly, the virus will remain passive on the host until it somehow executes the infected program, and then it will show its true colors. And by true colors, it can do serious damage to system software, corrupt files, steal passwords, permanently wipe data and even take over the entire system.

10. Sasser

Written by Sven Jaschan, a 17-year-old computer science student from Germany, this virus was so deadly that a $250,000 bounty was placed on the creator's head. Sasser was first discovered in 2004 as a Windows worm that slowed down and crashed the computer, only to restart after cutting the power connection. Sasser exploited a buffer overflow vulnerability in the Local Security Authority Subsystem Service (LSASS), which controls the security policy of local accounts, causing the computer to crash.

9. Flashback

We all know Macs as the epitome of privacy and security. The Trojan called Flashback proved otherwise, proving that even Macs are not immune. First discovered in 2011 by the antivirus company Intego, this Trojan horse tricked users into installing it by posing as an Adobe Flash installer.

8. Stuxnet

It was a multi-part worm that spread across Microsoft Windows PCs and traveled on USB drives. He looked for PLCs (specifically because of the presence of Siemens Step 7 software; software used by PLCs to automate and monitor electromechanical hardware).

7. CryptoLocker

CryptoLocker was a Trojan ransomware attack that infected more than 500,000 computers running on Windows. It encrypted the files and displayed a red ransom note asking for money in exchange for the encryption/unlock key. (And we think only the hijackers asked for ransom) The ransom demanded was usually $400 in prepaid cash or bitcoin.

6. Conficker

Also known as Downup/Downadup, it works by exploiting a network service issue present in Windows. Upon infection, the worm would change account lockout policies, block Windows updates, and log out user accounts, among many other routes. Eventually, the system would become a botnet slave and scam users out of money.

5. Code Red

This worm targeted systems with the Microsoft IIS web server installed and took advantage of a buffer overflow problem on the system. Code Red had a huge multiplicity, as it created hundreds and thousands of copies of itself, consuming a lot of system resources. Interestingly, it displayed the message - Hacked By Chinese on the affected web pages.

4. Zeus

Zeus, also known as Zbot, is a crimeware kit designed to steal users' online banking details and other important information to transfer money to secret bank accounts. It hit the web in 2007 and immediately picked up speed, being the reason for 44% of all banking malware attacks in the next 3 years.

3. WannaCry

It spreads using the EternalBlue exploit leaked by the National Security Agency (NSA). The exploit allows an attacker to transfer crafted packets to any device that accepts data from the public Internet on port 445. Once a system is infected, the worm multiplies and affects other unpatched devices, without the need for human interaction.

2. I LOVE YOU

The next time you receive a love letter, be careful because it could contain a virus. Jokes aside, the ILOVEYOU virus, also known as the love bug, is believed to be one of the most malicious and virulent computer viruses ever created on the face of the planet. He knocked on the user's door in the form of an email with the subject "I love you." The message contained an attachment 'LOVE-LETTER-TO-YOU.txt.vbs. Windows at the time could not display the actual extension of the file and users were stuck considering it to be a plain text file. Once opened, Visual Basic Script would activate and take over the local computer by overwriting the files itself and rendering the computer unbootable. It would also send itself to the user's entire mailing list, thus spreading much faster than any other email worm.

1. MyDoom

It worked similarly to the love bug; scraping email addresses from infected Windows computers and sending a new version of itself to those contacts. Every time the attachment was opened, the virus spread to more and more victims.