There are different viruses released with different malware intensions, out of which following are the 10 most dangerous viruses identified of all times. https://antivirus.comodo.com/faq/antivirus/what-is-the-most-dangerous-virus-in-my-computer/

1. 10 MOST DANGEROUS COMPUTER
VIRUSES
DIFFERENT VIRUSES RELEASED WITH DIFFERENT MALWARE INTENSIONS!

2. Click here to know more about Dangerous
viruses

3. ILOVEYOU
VIRUS
IT MANAGED TO WRECK HAVOC ON COMPUTER
SYSTEMS ALL OVER THE WORLD WITH AROUND
$10 BILLION WORTH OF DAMAGES.

4. MELISSA VIRUS
MELISSA ARRIVES IN AN ATTACHMENT TO AN E-MAIL NOTE
WITH THE SUBJECT LINE "IMPORTANT MESSAGE FROM
]THE NAME OF SOMEONE[," AND BODY TEXT THAT READS
"HERE IS THAT DOCUMENT YOU ASKED FOR...DON'T
SHOW ANYONE ELSE ;-)".

5. SASSER VIRUS
SASSER IS A COMPUTER WORM THAT AFFECTS
COMPUTERS RUNNING VULNERABLE VERSIONS OF THE
MICROSOFT OPERATING SYSTEMS WINDOWS XP AND
WINDOWS 2000. SASSER SPREADS BY EXPLOITING THE
SYSTEM THROUGH A VULNERABLE PORT.

6. ZUES VIRUS
ZEUS VIRUS (OR ZEUS TROJAN
MALWARE) IS A FORM OF MALICIOUS
SOFTWARE THAT TARGETS MICROSOFT
WINDOWS AND IS OFTEN USED TO
STEAL FINANCIAL DATA.

7. CONFICKER
VIRUS
CONFICKER IS A FAST-SPREADING WORM
THAT TARGETS A VULNERABILITY (MS08-067)
IN WINDOWS OS..

8. STUXNET
VIRUS
STUXNET TARGETS SCADA SYSTEMS AND IS
BELIEVED TO BE RESPONSIBLE FOR CAUSING
SUBSTANTIAL DAMAGE TO IRAN'S NUCLEAR
PROGRAM.

9. MYDOOM
VIRUS
THE MYDOOM VIRUS (ALSO
KNOWN AS A WORM AND AS
WIN32.MYDOOM.A) WAS A
VERY DAMAGING COMPUTER
VIRUS THAT AFFECTED
MICROSOFT WINDOWS-BASED
COMPUTERS.

10. AMITI
ANTIVIRUS

11. CRYPTOLOCKER
CRYPTOLOCKER IS A MALWARE THREAT
THAT GAINED NOTORIETY OVER THE
LAST YEARS. IT IS A TROJAN HORSE THAT
INFECTS YOUR COMPUTER AND THEN
SEARCHES FOR FILES TO ENCRYPT.

12. FLASHBACK
FLASHBACK VIRUS - A MALICIOUS TROJAN HORSE WHICH TARGETS MAC OS X USERS.