5: SQL Slammer/Sapphire

In late January 2003, a new Web server virus spread across the Internet. Many computer networks were unprepared for the attack, and as a result the virus brought down several important systems. The Bank of America's ATM service crashed, the city of Seattle suffered outages in 911 service and Continental Airlines had to cancel several flights due to electronic ticketing and check-in errors.

The culprit was the SQL Slammer virus, also known as Sapphire. By some estimates, the virus caused more than $1 billion in damages before patches and antivirus software caught up to the problem [source: Lemos]. The progress of Slammer's attack is well documented. Only a few minutes after infecting its first Internet server, the Slammer virus was doubling its number of victims every few seconds. Fifteen minutes after its first attack, the Slammer virus infected nearly half of the servers that act as the pillars of the Internet [source: Boutin].

The Slammer virus taught a valuable lesson: It's not enough to make sure you have the latest patches and antivirus software. Hackers will always look for a way to exploit any weakness, particularly if the vulnerability isn't widely known. While it's still important to try and head off viruses before they hit you, it's also important to have a worst-case-scenario plan to fall back on should disaster strike.
A Matter of Timing

Some hackers program viruses to sit dormant on a victim's computer only to unleash an attack on a specific date. Here's a quick sample of some famous viruses that had time triggers:

* The Jerusalem virus activated every Friday the 13th to destroy data on the victim computer's hard drive
* The Michelangelo virus activated on March 6, 1992 -- Michelangelo was born on March 6, 1475
* The Chernobyl virus activated on April 26, 1999 -- the 13th anniversary of the Chernobyl meltdown disaster
* The Nyxem virus delivered its payload on the third of every month, wiping out files on the victim's computer

Computer viruses can make a victim feel helpless, vulnerable and despondent. Next, we'll look at a virus with a name that evokes all three of those feelings.