6: Nimda

Another virus to hit the Internet in 2001 was the Nimda (which is admin spelled backwards) worm. Nimda spread through the Internet rapidly, becoming the fastest propagating computer virus at that time. In fact, according to TruSecure CTO Peter Tippett, it only took 22 minutes from the moment Nimda hit the Internet to reach the top of the list of reported attacks [source: Anthes].

The Nimda worm's primary targets were Internet servers. While it could infect a home PC, its real purpose was to bring Internet traffic to a crawl. It could travel through the Internet using multiple methods, including e-mail. This helped spread the virus across multiple servers in record time.

The Nimda worm created a backdoor into the victim's operating system. It allowed the person behind the attack to access the same level of functions as whatever account was logged into the machine currently. In other words, if a user with limited privileges activated the worm on a computer, the attacker would also have limited access to the computer's functions. On the other hand, if the victim was the administrator for the machine, the attacker would have full control.

The spread of the Nimda virus caused some network systems to crash as more of the system's resources became fodder for the worm. In effect, the Nimda worm became a distributed denial of service (DDoS) attack.
Phoning it In

Not all computer viruses focus on computers. Some target other electronic devices. Here's just a small sample of some highly portable viruses:

* CommWarrior attacked smartphones running the Symbian operating system (OS).
* The Skulls Virus also attacked Symbian phones and displayed screens of skulls instead of a home page on the victims' phones.
* RavMonE.exe is a virus that could infect iPod MP3 devices made between Sept. 12, 2006, and Oct. 18, 2006.
* Fox News reported in March 2008 that some electronic gadgets leave the factory with viruses pre-installed -- these viruses attack your computer when you sync the device with your machine [source: Fox News].


Next, we'll take a look at a virus that affected major networks, including airline computers and bank ATMs.