Conficker
In November 2008, a worm quietly sounded the geek alarms as it set about to infect millions of personal computers around the internet -- to date, estimated at 6-7 million. It was christened Conficker by MS security staff. It exploited a flaw in MS Windows operating systems -- got into the computer, closed the flaw, and went about replicating itself. It communicates to its home base with an encryption level that is so powerful, it's still in the lab -- and is one of the contenders for a new security standard to be published in 2013. It is part of a powerful botnet that was used only once, in what looks to have been designed to test its viability. Ever since then, it has sat dormant. Waiting. Not much is known about it's purpose or who controls it. What is known however is scary, because there is no way to stop it, and it can be used to cause severe disruption if needed. The good guys put up a good fight, but may have lost to the bad guys on this one -- but no one knows ...