The worst computer virus in history was the MyDoom computer virus in 2004.
The 2004 MyDoom computer virus cost damage that cost $38 billion and spread fast and overloaded servers and also created massive botnets for DDoS attacks.
The 2004 MyDoom computer virus spread rapidly through email attachments and turned infected computers into zombies.
Another worst computer virus in history was the 2017 WannaCry virus.
The 2017 WannaCry virus was a ransomware attack which affected over 200,000 computers in 150 countries, which disrupted healthcare like UK's NHS and even businesses.
The 2017 WannaCry virus encrypted files and demanded ransom payments, and exploited a Windows vulnerability.
And another worst computer virus in history was the 2010 Stuxnet virus.
The Stuxnet 2010 computer virus was a highly sophisticated computer virus worm that physically damaged Iranian nuclear centrifuges, which marked the first cyberweapon targeting industrial control systems.
The Stuxnet 2010 computer virus worm exploited multiple zero-day vulnerabilities to infiltrate Siemens control systems.
And finally another very bad worst computer virus in history was the ILOVEYOU virus that occurred in 2000.
The 2000 ILOVEYOU computer virus infected millions of computers within days and overwrote files and cost billions of dollars, which taught the world about social engineering via email.
The MyDoom computer virus was the absolute worst in history for it's sheer scale and economic cost.
The WannaCry computer virus was also worst in history for it's widespread ransomware impact.
The Stuxnet computer virus was worst in history for demonstrating cyber warfare's ability to cause physical damage.