About computer viruses

All viruses are terrible, especially the ones you accidentally get (which happens quite often), but these look the worst ever:

Melissa
It behaves tempting recipients into opening a document with an e-mail message like "Here is that document you asked for, don't show it to anybody else." Once activated, the virus replicates itself and sends itself out to the top 50 people in the recipient's e-mail address book.

I Love You
Also this one comes as an email like a love letter from a secret admirer.
The attachment is the one that causes all troubles.
(adding new files to the victim's registry keys, replacing several different kinds of files with copies of itself, stealing application that e-mailed secret information to the hacker's e-mail address.)

The Klez Virus
Usual email message, replicating itself and addressing all the people on the recipient's address book.
Later they added the "spoofing" (the e-mail appears to come from one source when it's really coming from somewhere else.)
Used for spamming could clog an inbox.

Code Red and Code Red II
It caused the buffer overflow problem, which means when a machine running on these operating systems receives more information than its buffers can handle, it starts to overwrite adjacent memory.
It initiated a distributed denial of service (DDoS) attack on the White House. That means all the computers infected with Code Red tried to contact the Web servers at the White House at the same time, overloading the machines.
The worm creates a backdoor into the computer's operating system, allowing a remote user to access and control the machine.
The person behind the virus can access information from the victim's computer or even use the infected computer to commit crimes.

Nimda
Its primary targets were Internet servers. While it could infect a home PC, its real purpose was to bring Internet traffic to a crawl.
The Nimda worm created a backdoor into the victim's operating system.

SQL Slammer/Sapphire
It caused more than $1 billion in damages before patches and antivirus software caught up to the problem.

SQL Slammer/Sapphire
It is another worm that can create a backdoor in the victim computer's operating system.
It spread through e-mail and peer-to-peer networks. According to the security firm MessageLabs, one in every 12 e-mail messages carried the virus at one time.

Sasser and Netsky
The Sasser worm attacked computers through a Microsoft Windows vulnerability. Unlike other worms, it didn't spread through e-mail. Instead, once the virus infected a computer, it looked for other vulnerable systems. It contacted those systems and instructed them to download the virus.
The Netsky virus moves through e-mails and Windows networks. It spoofs e-mail addresses and propagates through a 22,016-byte file attachment.


Some hackers program viruses to sit dormant on a victim's computer only to unleash an attack on a specific date.

Be prepared for a worst case scenario, because the danger is ALWAYS there.