The following are of some of the many viruses that are considered "the worst of the worst" to be unleashed upon the Internet.
Brian is the first computer virus that was created in 1986. It was from Pakistan and it only infected some floppy disks. It really didn't hurt your computer, but it did give bad ideas to over 100,000 virus creators and hackers for the next two decades.
The Michelangelo virus entered your hard drive and any floppy drive inserted into the computer causing it to spread very rapidly. After it spread quietly for months, it became active on March 6 - Michelangelo's birthday - and started destroying data on thousands of computers.
Technically a worm, Melissa collapsed entire email systems by causing computers to send mountains of messages to each other. The author of the virus, David L. Smith, was eventually caught and was sentenced twenty months in prison.
This was one of the first viruses to trick users into opening a file similar to the effects of a Trojan Horse, which claimed to be a love letter. It sent mountains of spam and junk mail then deleted thousands of files. Some estimates believe that 10% of all computers were affected by the ILOVEYOU virus and caused over 5.5 billion dollars of damage and is believed to be the worst worm of all time.
Code Red, 2001
Code Red was an early "blended threat" attack. It targeted Web servers and damaged websites and launching attacks on a host of IP addresses, including those of the White House.
It was built on Code Red's attack system of finding many paths into a computer such as email, websites, network connections, etc. It infected both Web servers and personal computers. It found paths into computers so effectively that after about 20 minutes when it was released, it became the Internet's most widespread virus at the time.
As an email virus, the Klez virus created the technque of spoofing the "From" field in an email message that it sent. Spoofing means that the email appears to come from one source, but really came from another.
MyDoom is noted as the fastest spreading email virus of all time. It created a backdoor in the in the infected computer's operating system allowing other viruses and malicious programs to enter the infected computer. Then it infected computers so they would send even more junk mail to other computers. Eventually, search engines like Google began to receive millions of search requests from the infected computers that slowed down search engine services and caused some to crash.
Storm Worm, 2007
The Strom Worm is one of the worst viruses of recent times. It is a Trojan Horse program and spread via email spam with a fake attachment and ultimately infected over 10 million computers, causing them to join its zombie botnet (a botnet is a collection of software robots that run automatically and autonomously). The public began to call the virus the Storm Worm because one of the email messages that carried the virus had a subject "230 dead as storm batters Europe." There is already a 2001 virus called the W32.Storm.Worm so the 2001 virus and the 2007 worm are not to be confused because they are completely different programs.